Exfoliating method, transferring method of thin film device, and thin film device, thin film integrated circuit device, and liquid crystal display device produced by the same

ABSTRACT

A transferring method including providing a substrate, forming a transferred layer over the substrate, joining a transfer member to the transferred layer, and removing the transferred layer from the substrate. The transferring method further includes transferring the transferred layer to the transfer member and reusing the substrate for another transfer. The transferring method may also include providing a substrate, forming a separation layer over the substrate, forming a transferred layer over the separation layer, and partly cleaving the separation layer such that a part of the transferred layer is transferred to a transfer member in a given pattern. The transferring method may also include joining a transfer member to the transferred layer, removing the transferred layer from the substrate and transferring the transferred layer to the transfer member, these of which constitute a transfer process, the transfer process being repeatedly performed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Division of application Ser. No. 10/851,202 filed May 24,2004, which in turn claims benefit of Ser. No. 10/420,840 filed Apr. 23,2003, which in turn claims the benefit of U.S. application Ser. No.10/091,562 filed Mar. 7, 2002, which in turn claims the benefit of U.S.patent application Ser. No. 09/051,966 filed Apr. 24, 1998, which is acontinuation of National Stage of PCT/JP97/02972 filed Aug. 26, 1997.The entire disclosures of the prior applications are hereby incorporatedby reference herein in their entirety.

BACKGROUND

The present invention relates to a method for exfoliating a detachedmember, and in particular, a transferring method for exfoliating atransferred layer comprising a thin film such as a functional thin filmand for transferring it onto a transfer member such as a transparentsubstrate. Also, the present invention relates to a transferring methodof a thin film device, a thin film device, a thin film integratedcircuit device, and a liquid crystal display device produced using thesame.

Production of liquid crystal displays using thin film transistors(TFTs), for example, includes a step for forming thin film transistorson a transparent substrate by a CVD process or the like.

The thin film transistors are classified into those using amorphoussilicon (a-Si) and those using polycrystalline silicon (p-Si), and thoseusing polycrystalline silicon are classified into those formed by a hightemperature process and those formed by a low temperature process.

Since the formation of such thin film transistors on a substrateinvolves treatment at a relatively high temperature, a heat resistantmaterial, that is, a material having a high softening point and a highmelting point must be used as the transparent substrate. At present, inthe production of TFTs by high temperature processes, transparentsubstrates composed of quartz glass which are sufficiently resistive toa temperature of approximately 1,000° C. are used. When TFTs areproduced by low temperature processes, the maximum process temperatureis near 500° C., hence heat-resisting glass which is resistive to atemperature near 500° C. is used.

As described above, a substrate for use in forming thin film devicesmust satisfy the conditions for producing these thin film devices. Theabove-mentioned “substrate” is, however, not always preferable in viewof only the steps after fabrication of the substrate provided with thinfilm devices is completed.

For example, in the production process with high temperature treatment,quartz glass or heat-resisting glass is used, however, they are rare andvery expensive materials, and a large transparent substrate can barelybe produced from the material.

Further, quartz glass and heat-resisting glass are fragile, easilybroken, and heavy. These are severe disadvantages when a substrateprovided with thin film devices such as TFTs is mounted into electronicunits. There is a gap between restriction due to process conditions andpreferred characteristics required for products, hence it issignificantly difficult to satisfy both the restriction andcharacteristics.

The present invention has been achieved in view of such a problem, andhas an object to provide an exfoliating method, which permits easyexfoliation regardless of characteristics of the detached member andconditions for exfoliating, and transferring to various transfermembers. Another object is to provide a novel technology which iscapable of independently selecting a substrate used in production ofthin film devices and a substrate used when the product is used (asubstrate having preferable properties for use of the product). Afurther object is to provide a novel technology not causingdeterioration of characteristics of thin film devices which aretransferred onto a substrate, by decreasing the optical energy radiatedto the separable layer causing ablation in the transferring process.

SUMMARY

1. First, a method for exfoliating a detached member or a transferredlayer from a substrate for production is disclosed. The inventions areas follows:

(1) An exfoliating method in accordance with the present invention is amethod for exfoliating a detached member, which is present on asubstrate with a separation layer therebetween, from the substrate,wherein the separation layer is irradiated with incident light so as tocause exfoliation in the separation layer and/or at the interface, andto detach the detached member from the substrate.

(2) A method for exfoliating a detached member, which is present on atransparent substrate with a separation layer therebetween, from thesubstrate, wherein the separation layer is irradiated with incidentlight from the side of the substrate so as to cause exfoliation in theseparation layer and/or at the interface, and to detach the detachedmember from the substrate.

(3) A method for exfoliating a transferred layer formed on a substratewith a separation layer therebetween from the substrate and transferringthe transferred layer onto a transfer member, wherein after the transfermember is adhered to the opposite side of the transferred layer to thesubstrate, the separation layer is irradiated with incident light so asto cause exfoliation in the separation layer and/or at the interface,and to detach the transferred layer from the substrate to transfer ontothe transfer member.

(4) A method for exfoliating a transferred layer formed on a transparentsubstrate with a separation layer therebetween from the substrate andtransferring the transferred layer onto a transfer member, wherein afterthe transfer member is adhered to the opposite side of the transferredlayer to the substrate, the separation layer is irradiated with incidentlight from the side of the substrate so as to cause exfoliation in theseparation layer and/or at the interface, and to detach the transferredlayer from the substrate to transfer onto the transfer member.

(5) An exfoliating method includes a step for forming a separation layeron a transparent substrate, a step for forming a transferred layer onthe separation layer directly or with a given interlayer therebetween, astep for adhering the transfer member to the opposite side of thetransferred layer to the substrate, and a step for irradiating theseparation layer with incident light from the side of the substrate soas to cause exfoliation in the separation layer and/or at the interface,and to detach the transferred layer from the substrate to transfer ontothe transfer member.

In connection with these inventions, the following inventions aredisclosed.

After transferring the transferred layer onto the transfer member, astep for removing the separation layer adhering to the side of thesubstrate and/or transfer member may be provided.

A functional thin film or a thin film device may be used as thetransferred layer. Particularly, a thin film transistor is preferablyused as the transferred layer. Preferably, the transfer member is atransparent substrate.

When the maximum temperature in the formation of the transferred layeris Tmax, it is preferred that the transfer member be composed of amaterial having a glass transition point (Tg) or softening point whichis lower than Tmax. Particularly, it is preferred that the transfermember be composed of a material having a glass transition point (Tg) orsoftening point which is lower than 800° C.

It is preferable that the transfer member be composed of a syntheticresin or glass.

It is preferable that the substrate has thermal resistance. Inparticular, when the maximum temperature in the formation of thetransferred layer is Tmax, it is preferred that the substrate becomposed of a material having a distortion point which is lower thanTmax.

In the above-mentioned exfoliating methods, the exfoliation of theseparation layer is caused by an elimination of or a decrease in theadhering force between atoms or molecules in the constituent substancesin the separation layer.

It is preferable that the incident light be laser light. Preferably, thelaser light has a wavelength of 100 nm to 350 nm. Alternatively, thelaser light has a wavelength of 350 nm to 1,200 nm.

It is preferable that the separation layer is composed of amorphoussilicon. Preferably, the amorphous silicon contains 2 atomic percent ormore of hydrogen (H).

The separation layer may be composed of a ceramic. Alternatively, theseparation layer may be composed of a metal. Alternatively, theseparation layer may be composed of an organic polymer. In this case, itis preferable that the organic polymer has at least one adhere selectedfrom the group consisting of —CH₂—, —CO—, —CONH—, —NH—, —COO—, —N═N—,and —CH═N—. Further, it is preferable that the organic polymer has anaromatic hydrocarbon group in the chemical formula.

2. Next, inventions in which the above-mentioned separation layerincludes a plurality of composites are disclosed. These inventions areas follows.

First, the separation layer in the inventions disclosed in paragraph 1includes a composite with a plurality of layers. Further, the separationlayer includes at least two layers having different compositions orcharacteristics.

It is preferable that the separation layer includes an opticalabsorption layer for absorbing the incident light and another layerhaving a different composition or property from the optical absorptionlayer. Preferably, the separation layer includes the optical absorptionlayer for absorbing the incident light and a shading layer for shadingthe incident light. Preferably, the shading layer lies at the oppositeside of the optical absorption layer to the incident light. Preferably,the shading layer is a reflection layer for reflecting the incidentlight. Preferably, the reflection layer is composed of a metallic thinfilm.

3. A method for transferring a thin film device, which is used as adetached member or a transferred member, will now be disclosed.

A method for transferring a thin film device on a substrate onto atransferred member includes: a step for forming a separation layer onthe substrate; a step for forming a transferred layer including the thinfilm device onto the separation layer; a step for adhering thetransferred layer including the thin film device to the transfer memberwith an adhesive layer, a step for irradiating the separation layer withlight so as to cause exfoliation in the separation layer and/or at theinterface; and a step for detaching the substrate from the separationlayer.

In accordance with the present invention, for example, a separationlayer having optical absorption characteristics is provided on asubstrate having high reliability in device production, and thin filmdevices such as TFTs and the like are formed on the substrate. Next,although not for limitation, the thin film devices are adhered to agiven transfer member, for example, with an adhesive layer, so as tocause an exfoliation phenomenon in the separation layer, which resultsin a decrease in adhering between the separation layer and thesubstrate. The substrate is detached from the thin film devices by theforce applied to the substrate. A given device with high reliability canbe thereby transferred or formed onto any transfer members.

In the present invention, either the step for adhering the thin filmdevices (the transferred layer including the thin film devices) to thetransfer member with the adhesive layer or the step for detaching thesubstrate from the thin film devices may precede. When handling of thethin film devices (the transferred layer including the thin filmdevices) after detaching the substrate is troublesome, however, it ispreferable that the thin film devices be adhered to the transfer member,and then the substrate be detached.

When an adhesive layer for adhering the thin film devices to thetransfer member is, for example, a substance having planation, theuneven face formed on the surface of the transferred layer including thethin film devices is negligible by the planation, the adhering to thetransfer member is satisfactorily performed. The substrate may be atransparent substrate, and thus the separation layer is irradiated withthe light through the transparent substrate. The use of, for example, atransparent substrate, e.g. a quartz substrate, permits production ofthin film devices with high reliability and collective irradiation ofthe entire separation layer with the light from the rear side of thesubstrate, resulting in an improvement in the transfer efficiency.

4. Inventions in which parts of the steps, disclosed in theabove-mentioned paragraph 3, in the method for transferring the thinfilm device will now be disclosed. These inventions are as follows:

(1) A method for transferring a transferred layer including a thin filmdevice forming on a substrate onto a transfer member comprising: a firststep for forming an amorphous silicon layer on the substrate; a secondstep for forming the transferred layer including the thin film device onthe amorphous silicon layer; a third step for adhering the transferredlayer including the thin film device to the transfer member with anadhesive layer; a fourth step for irradiating the amorphous siliconlayer with light through the substrate so as to cause exfoliation in theamorphous silicon layer and/or at the interface and to decrease theadhering force between the substrate and the transferred layer; and afifth step for detaching the substrate from the amorphous silicon layer;wherein the transferred layer formed in the second step includes a thinfilm transistor, and the thickness of the amorphous silicon layer formedin the first step is smaller than the thickness of the channel layer ofthe thin film transistor formed in the second step.

In this invention, the amorphous silicon layer is used as the layerformed on the substrate in the first step and causes exfoliation bylight irradiation. In the amorphous silicon layer as shown in FIG. 39,optical energy, which is radiated in the amorphous silicon layer andwhich is required for exfoliation (referred to as ablation in FIG. 39),decreases as the thickness decreases.

The transferred layer formed in the second step includes the thin filmtransistor as a thin film device, its channel layer is formed ofsilicon, e.g., polycrystalline silicon or amorphous silicon, and thetransferred layer has a thickness of more than 25 nm, for example,approximately 50 nm. In this invention, the thickness of the amorphoussilicon as the separation layer (ablation layer) formed in the firststep is smaller than that of the channel layer of the thin filmtransistor in the transferred layer. The energy consumed in the lightirradiation step therefore decreases, and the light source can beminiaturized. Further, since optical energy by irradiation is low, thedeterioration of the thin film device is suppressed if the light leakedfrom the amorphous silicon layer is incident on the thin film device.

Now, the thickness of the amorphous silicon layer is set to 25 nm orless. As described above, the optical energy, which is radiated in theamorphous silicon layer and which is required for exfoliation, decreasesas the thickness decreases, hence the optical energy is significantlylow at this thickness. It is preferable that the thickness of theamorphous silicon layer be in a range from 5 nm to 25 nm, morepreferably 15 nm or less, and most preferably 11 nm or less in order tofurther decrease the optical energy, which is radiated in the amorphoussilicon layer and which is required for exfoliation.

In the second step, the amorphous silicon layer is formed by a lowpressure chemical vapor deposition (LPCVD) process. The amorphoussilicon layer formed by the LPCVD process has a higher adhesion comparedwith a plasma CVD process, an atmospheric pressure (AP) CVD process, oran ECR process, hence there is not much risk of failures, such asevolution of hydrogen and flaking of the film, during the formation ofthe transferred layer including the thin film device.

(2) A method for transferring a transferred layer including a thin filmdevice on a substrate onto a transfer member comprising: a step forforming a separation layer onto the substrate; a step for forming asilicon-based optical absorption layer on the separation layer; a stepfor forming the transferred layer including the thin film device on thesilicon-based optical absorption layer; a step for adhering thetransferred layer including the thin film device to the transfer memberwith an adhesive layer; a step for irradiating the separation layer withlight through the substrate so as to cause exfoliation in the separationlayer and/or at the interface; and a step for detaching the substratefrom the separation layer.

In accordance with this invention, if light leaks from the separationlayer, the leaked light is absorbed in the silicon-based opticalabsorption layer before it is incident on the thin film device. No lightis therefore incident on the thin film device, hence the thin filmdevice is prevented from characteristic deterioration due to theincident light. The transferred layer including the thin film device canbe formed on the silicon-based optical absorption layer. Metalliccontamination will therefore not occur as in the case forming thetransferred layer onto a metallic layer reflecting light, and the thinfilm device can be formed by an established thin film depositiontechnology.

The separation layer and the optical absorption layer are formed ofamorphous silicon, and a step for providing a silicon-based interveninglayer between the separation layer and the optical absorption layer. Asshown in FIG. 39, the amorphous silicon layer, which absorbs theincident light and separates when the energy of the absorbed lightreaches a given value, is used as the separation layer and thesilicon-based optical absorption layer. As the intervening layer forseparating the two amorphous silicon layers, a silicon compound, forexample, silicon oxide, is used.

(3) A method for transferring a transferred layer including a thin filmdevice on a substrate onto a transfer member comprising: a first stepfor forming a separation layer on the substrate; a second step forforming the transferred layer including the thin film device on theseparation layer; a third step for adhering the transferred layerincluding the thin film device to the transfer member with an adhesivelayer; a fourth step for irradiating the separation layer with lightthrough the substrate so as to cause exfoliation in the separation layerand/or at the interface; and a fifth step for detaching the substratefrom the separation layer; wherein, in the fourth step, the stress,acting on the upper layers above the separation layer in the exfoliationin the separation layer and/or at the interface, is absorbed by theproof stress of the upper layers above the separation layer to preventthe deformation or breakage of the upper layers above the separationlayer.

In the fourth step, the substances in the separation layer are opticallyor thermally excited by the incident light to cut bonds of atoms ormolecules on the surface and in the interior and liberate the moleculesand atoms to the exterior. This phenomenon is observed as phasetransition, such as melting or evaporation, of the partial or entiresubstances in the separation layer. A stress acts on the upper layersabove the separation layer as the molecules or atoms are released. Thestress is, however, absorbed by the proof stress of the upper layersabove the separation layer so as to prevent deformation or breakage ofthe upper layers above the separation layer.

The materials and/or thicknesses of the upper layers above theseparation layer may be designed in view of such a proof stress. Forexample, one or more among the thickness of the adhesive layer, thethickness of the transferred layer, the material, and the thickness ofthe transfer member is designed in view of the proof stress.

Before performing the fourth step, the method further includes a stepfor forming a reinforcing layer for ensuring the proof stress at anyposition among the upper layers above the separation layer. In thisinvention, if the proof stress is not ensured only by the minimumconfiguration of the upper layers above the separation layer, consistingof the adhesive layer, the transferred layer, and the transfer member,deformation and breakage of the thin film device is prevented by addingthe reinforcing layer.

(4) A method for transferring a transferred layer including a thin filmdevice on a substrate onto a transfer member comprising: a first stepfor forming a separation layer on the substrate; a second step forforming the transferred layer including the thin film device on theseparation layer; a third step for adhering the transferred layerincluding the thin film device to the transfer member with an adhesivelayer; a fourth step for irradiating the separation layer with lightthrough the substrate so as to cause exfoliation in the separation layerand/or at the interface; and a fifth step for detaching the substratefrom the separation layer; wherein, the fourth step includes sequentialscanning of beams for locally irradiating the separation layer, suchthat a region irradiated by the N-th beam (wherein N is an integer of 1or more) does not overlap with other irradiated regions.

In the fourth step, beams, such as spot beams or line beams, for locallyirradiating the separation layer are intermittently scanned so thatsubstantially all the surface of the separation layer is irradiated withlight. The beam scanning is achieved by relative movement between thesubstrate provided with the separation layer and the beam source or itsoptical system, and irradiation may be continued or discontinued duringthe relative movement. In this invention, the intermittent beam scanningis performed so that the adjacent beam-irradiated regions do not overlapwith each other.

If the beam-irradiated regions overlap, the region may be irradiatedwith an excessive amount of light which will cause exfoliation in theseparation layer or at the interface. It is clarified by analysis by thepresent inventor that an excessive amount of light partially leaks, isincident on the thin film device, and causes the deterioration ofelectrical characteristics and the like of the thin film device.

In the present invention, the separation layer is irradiated with suchan excessive amount of light, hence the original characteristics of thethin film device are maintained after the thin film device istransferred onto the transfer member. A zone between individualbeam-irradiated regions may be a low irradiation zone in which light isincident during the relative movement or a non-irradiation zone in whichno light is incident during the relative movement. Exfoliation does notoccur in the low irradiation zone or non-irradiation zone, the adhesionbetween the separation layer and the substrate can be remarkablyreduced.

In the following two inventions, each beam for preventing or suppressingthe characteristic deterioration of the thin film device is determinedin different views from the invention in paragraph (4).

In the fourth step of the first invention, beams are sequentiallyscanned to irradiate locally the separation layer, each beam has a flatpeak region having the maximum optical intensity in the center, and aregion irradiated by the N-th beam (wherein N is an integer of 1 ormore) does not overlap with other irradiated regions.

In the fourth step of the other invention, beams are sequentiallyscanned to irradiate locally the separation layer, each beam has themaximum optical intensity in the central region, and an effective regionirradiated by the N-th beam (wherein N is an integer of 1 or more)having an intensity, which is 90% or more of the maximum intensity, doesnot overlap with the other effective regions irradiated by other beamscanning.

Since individual beams are scanned so that the flat peaks of individualbeams or the effective regions having intensities which are 90% or moreof the maximum intensity do not overlap with each other, two beams arecontinuously scanned in the same region in the separation layer.

The total irradiated beam (sum of the optical intensity x time) in thesame region is lower than that when the flat peak region or theeffective region having intensities which are 90% or more of the maximumintensity is set at the same position in the two consecutively scannedbeams. As a result, the separation layer may separate after the secondscanning in some regions, and this case does not correspond to theexcessive irradiation. In another case, even if the separation layerseparates in the first scanning, the intensity of the light incident onthe thin film device in the second scanning is decreased, hence thedeterioration of the electric characteristics of the thin film devicecan be prevented or reduced.

In the thin film device formed on a given substrate by a transfertechnology of the thin film device (the thin film structure) inaccordance with the present invention, the deterioration of variouscharacteristics can be prevented or reduced by improving the irradiatingstep for exfoliating the separation layer.

When the thin film device is a thin film transistor (TFT), the improvedirradiation step for exfoliating the separation layer can prevent thebreakdown of the TFT due to a decreased on-current flow and an increasedoff-current flow in the channel layer of the TFT damaged by the incidentlight.

5. Further, the following inventions are disclosed in connection withthe above-mentioned inventions.

A step for removing the separation layer adhered to the transfer memberis provided for completely removing the unnecessary separation layer.

The transfer member is a transparent substrate. For example, inexpensivesubstrates such as a soda glass substrate and flexible transparentplastic films may be used as the transfer member. When the maximumtemperature of the transfer member during the formation is Tmax, thetransfer member is composed of a material having a glass transitionpoint (Tg) or softening point which is lower than Tmax.

Although such inexpensive glass substrates etc. have not been usedbecause they are not resistive to the maximum temperature of theconventional device production processes, they can be used in thepresent invention without restriction.

The glass transition point (Tg) or softening point of the transfermember is lower than the maximum temperature in the process for formingthe thin film device. The upper limit of the glass transition point (Tg)or softening point is defined. The transfer member is composed of asynthetic resin or a glass material. For example, when the thin filmdevice is transferred onto a flexible synthetic resin plate such as aplastic film, excellent characteristics which are not obtainable in aglass substrate with high rigidity can be achieved. When the presentinvention is applied to a liquid crystal device, a flexible lightweightdisplay device which is resistive to falling can be achieved.

Also, a thin film integrated circuit such as a single-chip microcomputerincluding TFTs can be formed by transferring the TFTs on a syntheticresin substrate by the above-mentioned transferring method.

An inexpensive substrate such as a soda-glass substrate can also be usedas the transfer member. A soda-glass substrate is inexpensive and thushas economical advantages. Since alkaline components are dissolved fromthe soda-glass substrate during annealing of the TFT production, it hasbeen difficult to apply active matrix liquid crystal display devices. Inaccordance with the present invention, however, since a completed thinfilm device is transferred, the above-mentioned problems caused by theannealing will not occur. Accordingly, substrates having problems in theprior art technologies, such as a soda-glass substrate, can be used inthe field of active matrix liquid crystal display devices.

The substrate has thermal resistivity: The thin film device can beannealed at a high temperature in the production process, and theresulting thin film device has high reliability and high performance.

The substrate has a transmittance of 10% or more for the 310 nm light:The transparent substrate can supply optical energy sufficient toablation in the separation layer.

When the maximum temperature in the formation of the transferred layeris Tmax, the substrate is composed of a material having a distortionpoint of Tmax or more: The thin film device can be treated at a hightemperature in the production process, and the resulting thin filmdevice has high reliability and high performance.

The separation layer may be composed of amorphous silicon: The amorphoussilicon can absorb light, can be easily produced, and has a highlypractical use.

The amorphous silicon contains 2 atomic percent or more of hydrogen (H):When the amorphous silicon containing hydrogen is used, hydrogen isreleased by light irradiation, and an internal pressure occurs in theseparation layer to promote exfoliation in the separation layer. Theamorphous silicon may contain 10 atomic percent or more of hydrogen (H).The exfoliation in the separation layer is further accelerated by theincreased hydrogen content.

Alternatively, the separation layer may be composed of silicon nitride:When using silicon nitride as a separation layer, nitrogen is releasedby light irradiation to promote exfoliation in the separation layer.

Alternatively, the separation layer may be composed of ahydrogen-containing alloy: When using a hydrogen-containing alloy,hydrogen is released by light irradiation to promote exfoliation in theseparation layer.

Alternatively, the separation layer may be composed of anitrogen-containing alloy: When using a nitrogen-containing alloy,nitrogen is released by light irradiation to promote exfoliation in theseparation layer.

The separation layer may be composed of a multi-layered film: Theseparation layer is therefore not limited to a single-layered film. Themulti-layered film is composed of an amorphous silicon film and ametallic film formed thereon.

The separation layer may be composed of at least one material selectedfrom the group consisting of ceramics, metals, and organic polymers.Usable metals include, for example, hydrogen containing alloys andnitrogen containing alloys. As in amorphous silicon, exfoliation in theseparation layer is accelerated by the evolution of gaseous hydrogen ornitrogen by light irradiation.

The light is laser light. Laser light is coherent light and is suitablefor causing exfoliation in the separation layer. The laser light has awavelength of 100 nm to 350 nm. The short-wave, high energy laser lightresults in effective exfoliation in the separation layer. An example ofsuch a laser is an excimer laser. The excimer laser is a gas laser whichis capable of outputting laser light with high energy, and four typicaltypes of laser light can be output (XeF=351 nm, XeCl=308 nm, KrF=248 nm,ArF=193 nm) by combinations of rare gasses (Ar, Kr, and Xe) and halogengasses (F₂ and HCl) as laser media. By excimer laser irradiation directscission of molecular adheres and gas evolution will occur in theseparation layer provided on the substrate, without thermal effects.

The laser light may have a wavelength of 350 nm to 1,200 nm. For thepurpose of imparting exfoliation characteristics to the separation layerby changes, such as gas evolution, vaporization, and sublimation, laserlight having a wavelength of 350 nm to 1,200 nm can also be used.

The thin film device may be a thin film transistor (TFT). The TFT may bea CMOS-type TFT.

A high-performance TFT can be transferred (formed) on a given transfermember without restriction. Various electronic circuits can therefore bemounted on the transfer member. Accordingly, by the above-mentionedinventions, a thin film integrated circuit device including the thinfilm device transferred onto the transfer member is achieved. Also, aliquid crystal display device including an active matrix substrate,which is produced by the transfer of the thin film transistors in thepixel region, is achieved, wherein the pixel region includes a matrix ofthin film transistors and pixel electrodes each connected to one end ofeach thin film transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 8 are cross-sectional views of steps in a first embodiment ofan exfoliating method in accordance with the present invention.

FIGS. 9 to 16 are cross-sectional views of steps in a second embodimentof an exfoliating method in accordance with the present invention.

FIGS. 17 to 22 are cross-sectional views of steps in a third embodimentof a method for transferring a thin film device in accordance with thepresent invention.

FIG. 23 is a graph illustrating a change in the transmittance of a firstsubstrate (a substrate 100 in FIG. 17) to the wavelength of laser light.

FIGS. 24 to 34 are cross-sectional views of steps in a fourth embodimentof a method for transferring a thin film device in accordance with thepresent invention.

FIGS. 35(a) and 35(b) are isometric views of a microcomputer produced inaccordance with the present invention.

FIG. 36 is a schematic view illustrating a configuration of a liquidcrystal display device.

FIG. 37 is a schematic view illustrating a configuration of the mainsection in a liquid crystal display device.

FIG. 38 is a cross-sectional view of another embodiment of a method fortransferring a thin film device in accordance with the presentinvention.

FIG. 39 is a graph of a relationship between optical energy absorbed inthe separation layer and the thickness of the separation layer, forillustrating ablation in the separation layer which is composed ofamorphous silicon.

FIG. 40 is a cross-sectional view of another embodiment in which anamorphous silicon layer as an optical absorption layer is formed on anamorphous silicon layer as a separation layer with a silicon-basedintervening layer therebetween.

FIG. 41 is a cross-sectional view of another embodiment in which asilicon-based optical absorption layer composed of a material which isdifferent from that of a separation layer is formed on the separationlayer.

FIGS. 42(A) to 42(E) are cross-sectional views of another embodiment inwhich a reinforcing layer is provided to prevent deformation or breakageof a thin film device during exfoliation of a separation layer.

FIG. 43 is a schematic view illustrating a scanning operation of beamsonto a separation layer in a step in a method for transferring a thinfilm device in accordance with the present invention.

FIG. 44 is a plan view illustrating beam scanning in FIG. 42.

FIG. 45 is a schematic view illustrating another embodiment of ascanning operation of beams onto a separation layer in a step in amethod for transferring a thin film device in accordance with thepresent invention.

FIG. 46 is a graph of characteristic curves illustrating an intensitydistribution of beams used in the beam scanning shown in FIG. 45.

FIG. 47 is a graph of characteristic curves illustrating anotherintensity distribution of beams used in the beam scanning shown in FIG.45.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the exfoliating method in accordance with the presentinvention will now be described in detail with reference to the attacheddrawings.

First Embodiment

FIGS. 1 to 8 are cross-sectional views of steps in a first embodiment ofan exfoliating method in accordance with the present invention. Thesesteps in the exfoliating method (transferring method) in accordance withthe present invention will now be described.

[1] As shown in FIG. 1, a separation layer (optical absorption layer) 2is formed on one side (an inner surface 11 forming exfoliation) of asubstrate 1. It is preferable that the substrate 1 has transparency toallow indent light 7 to pass through from the side of the substrate 1.The transmittance of the incident light 7 is preferably 10% or more, andmore preferably 50% or more. A significantly low transmittance causes alarge loss of the incident light 7, hence a larger amount of light isrequired for exfoliation of the separation layer 2.

The substrate 1 is preferably composed of a material with highreliability, and particularly composed of a heat-resistant material.When forming a transferred layer 4 and an interlayer 3 as describedlater, a process temperature will increase depending on the types orformation processes (for example, from 350° C. to 1,000° C.). In such acase, if the substrate 1 has excellent heat resistance, the conditionsfor forming the films, such as a temperature, are widely changed in theformation of the transferred layer 4 and the like on the substrate 1.

When the maximum temperature in the formation of the transferred layer 4is Tmax, it is preferable that the substrate 1 be composed of a materialhaving a distortion point of Tmax. That is, it is preferable that thematerial for the substrate 1 has a distortion point of 350° C. or more,and more preferably 500° C. or more. Examples of such materials includeheat-resistant glass, such as quartz glass, soda glass, Corning 7059,and OA-2 made by Nippon Electric Glass Co., Ltd.

When the process temperature is decreased in the formation of theseparation layer 2, interlayer 3, and transferred layer 4, the substrate1 can be composed of an inexpensive glass material or synthetic resinhaving a lower melting point.

Although the thickness of the substrate 1 is not limited, it ispreferable that the thickness be generally about 0.1 to 5.0 mm, and morepreferably 0.5 to 1.5 mm. A remarkably small thickness of the substrate1 causes decreased mechanical strength, whereas an excessively largethickness causes a large loss of the incident light 7 if the substrate 1has a low transmittance. When the substrate 1 has a high transmittancefor the incident light 7, the thickness may be larger than theabove-mentioned upper limit.

It is preferable that the thickness of the substrate 1 at the portionfor forming the separation layer be uniform for achieving uniformirradiation by the incident light 7. The inner surface 11 forexfoliation and the light-incident surface 12 of the substrate are notlimited to the planar form, and may also be curved. In the presentinvention, the substrate 1 is not removed by etching etc., but thesubstrate 1 is removed by exfoliation in the separation layer 2 providedbetween the substrate 1 and the transferred layer 4, hence the operationis easy, and the substrate 1 has high selectivity, for example, arelatively high thickness.

The separation layer 2 will now be described. The separation layer 2absorbs the incident light 7 to cause exfoliation in the layer and/or atan interface 2 a or 2 b (hereinafter referred to as “internalexfoliation” and “interfacial exfoliation”). Irradiation by the incidentlight 7 causes an elimination or reduction of the adhering force betweenatoms or molecules in the constituent substance of the separation layer2, that is, ablation, and internal and/or interfacial exfoliation willoccur as a result. Further, in some cases, gas will be released from theseparation layer 2 by the incident light 7, resulting in theexfoliation. Consequently, there are two exfoliation mechanisms, thatis, releasing components contained in the separation layer 2 as gas, andinstantaneous vaporization of the separation layer 2 by absorption ofthe light followed by release of the vapor.

Examples of the composition for the separation layer 2 are the following(1) to (6):

(1) Amorphous Silicon (a-Si):

Amorphous silicon may contain hydrogen (H). In this case, it ispreferable that the hydrogen content be approximately 2 atomic percentor more, and more preferably 2 to 20 atomic percent. When a given amountof hydrogen is contained, hydrogen is released by irradiation of theincident light 7, and an internal pressure, which will act as a forcefor delaminating the upper and lower thin films, occurs in theseparation layer 2. The hydrogen content in the amorphous silicon can becontrolled by determining the film forming conditions, for example, thegas composition, gas pressures, gas atmospheres, gas flow rates,temperature, substrate temperature, and input power in the CVD process.

(2) Oxide Ceramics, Dielectrics (Ferroelectrics) and Semiconductors,such as Silicon Oxides and Silicates, Titanium Oxides and Titanates,Zirconium Oxide and Zirconates, and Lanthanum Oxide and Lanthanates:

Examples of silicon oxides include SiO, SiO₂, and Si₃O₂, and examples ofsilicates include K₂SiO₃, Li₂SiO₃, CaSiO₃, ZrSiO₄, and Na₂SiO₃. Examplesof titanium oxides include TiO, Ti₂O₃, and TiO, and examples oftitanates include BaTiO₄, BaTiO₃, Ba₂Ti₉O₂₀, BaTi₅O₁₁, CaTiO₃, SrTiO₃,PbTiO₃, MgTiO₃, ZrTiO₂, SnTiO₄, Al₂TiO₅, and FeTiO₃. Examples ofzirconium oxides include ZrO₂, and examples of zirconates includeBaZrO₃, ZrSiO₄, PbZrO₃, MgZrO₃, and K₂ZrO₃.

(3) Ceramics and Dielectrics (Ferroelectrics), such as PZT, PLZT, PLLZTand PBZT:

(4) Nitride Ceramics, such as Silicon Nitride, Aluminum Nitride, andTitanium Nitride:

(5) Organic Polymers:

Usable organic polymers have linkages (which are cut by irradiation ofthe incident light 7), such as —CH₂—, —CO— (ketone), —CONH— (amido),—NH— (imido), —COO— (ester), —N═N— (azo), and —CH═N— (isocyano). Inparticular, any organic polymers having large numbers of such linkagescan be used. The organic polymers may have aromatic hydrocarbon (one ormore benzene ring or fused ring) in the chemical formulae. Examples ofthe organic polymers include polyolefins, such as polyethylene, andpolypropylene; polyimides; polyamides; polyesters; polymethylmethacrylate (PMMA); polyphenylene sulfide (PPS); polyether sulfone(PES); and epoxy resins.

(6) Metals:

Examples of metals include Al, Li, Ti, Mn, In, Sn, Y, La, Ce, Nd, Pr,Gd, and Sm; and alloys containing at least one of these metals.

The thickness of the separation layer 2 depends on various conditions,such as the purpose for exfoliation, the composition of the separationlayer 2, the layer configuration, and the method for forming the layer,and has a thickness of generally about 1 nm to 20 μm, preferably about10 nm to 2 μm, and more preferably about 40 nm to 1 μm. A significantlysmall thickness requires a larger amount of incident light 7 in order tosecure excellent exfoliation characteristics of the separation layer 2,and an operational time for removing the separation layer 2 in thesucceeding step. It is preferable that the thickness of the separationlayer 2 be as uniform as possible.

The method for forming the separation layer 2 is not limited, and isdetermined depending on several conditions, such as the film compositionand thickness. Examples of the methods include vapor phase depositionprocesses, such as CVD (including MOCVD, low pressure CVD, ECR-CVD),evaporation, molecular beam (MB) evaporation, sputtering, ion-plating,and PVD; plating processes, such as electro-plating, dip-plating(dipping), and electroless-plating; coating process, such as aLangmuir-Blodgett process, spin-coating process, spray-coating process,and roll-coating process; printing processes; transfer processes;ink-jet processes; and powder-jet processes. A combination of theseprocesses may also be used. For example, when the separation layer 2 iscomposed of amorphous silicon (a-Si), it is preferable that the layer beformed by a low pressure CVD process or a plasma CVD process.Alternatively, when the separation layer 2 is composed of a ceramic by asol-gel process, or an organic polymer, it is preferable that the layerbe formed by a coating process, and particularly a spin-coating process.The separation layer 2 may be formed by two or more steps (for example,a layer-forming step and an annealing step).

[2] As shown in FIG. 2, an interlayer (underlying layer) 3 is formed onthe separation layer 2.

The interlayer 3 is formed for various purposes, for example, as aprotective layer which physically and chemically protects thetransferred layer 4 during production and use, an insulating layer, aconductive layer, a shading layer for the incident light 7, a barrierlayer prohibiting migration of components to or from the transferredlayer 4, and a reflection layer.

The composition of the interlayer 3 is determined by the purpose. Forexample, the interlayer 3, formed between the separation layer 2composed of amorphous silicon and the transferred layer 4 including athin film transistor, is composed of silicon oxides such as SiO₂.Alternatively, the interlayer 3, formed between the separation layer 2and the transferred layer 4 including PZT, is composed of a metal, suchas Pt, Au, W, Ta, Mo, Al, Cr, or Ti, or an alloy primarily containingsuch a metal. The thickness of the interlayer 3 is determined inresponse to the purpose and functions, and ranges generally from about10 nm to 5 μm, and preferably about 40 nm to 1 μm. The interlayer 3 maybe formed by the same method as for the separation layer 2. Theinterlayer 3 may be formed by two or more steps.

The interlayer 3 may include two or more layers having the samecomposition or different compositions. In the present invention, thetransferred layer 4 may be formed directly on the separation layer 2without forming the interlayer 3.

[3] As shown in FIG. 3, a transferred layer (detached member) is formedon the interlayer 3. The transferred layer 4 will be transferred onto atransfer member 6 later, and is formed by the same method as in theseparation layer 2.

The purpose for forming the transferred layer 4, and type, shape,structure, composition, and physical and chemical characteristics of thetransferred layer 4 are not limited, and it is preferable that thetransferred layer 4 be a thin film, and particularly a functional thinfilm or thin film device. Examples of functional thin films and thinfilm devices include thin film transistors; thin film diodes; other thinfilm semiconductor devices; electrodes (e.g. transparent electrodes suchas ITO and mesa films); photovoltaic devices used in solar batteries andimage sensors; switching devices; memories; actuators such aspiezoelectric devices; micromirrors (piezoelectric thin film ceramics);recording media such as magnetic recording media, magneto-opticalrecording media, and optical recording media; magnetic recording thinfilm heads, coils, inductors and thin film high permeability materials,and micro-magnetic devices composed of combinations thereof; opticalthin films such as filters, reflection films, dichroic mirrors, andpolarizers; semiconductor thin films; superconducting thin films, e.g.YBCO thin films; magnetic thin films; and multi-layered thin films, suchas metallic multi-layered thin films, metallic-ceramic multi-layeredthin films, metallic multi-layered semiconductor thin films, ceramicmulti-layered semiconductor thin films, and multi-layered thin filmsincluding organic layers and other layers. Among them, application tothin film devices, micro-magnetic devices, three-dimensionalmicro-articles, actuators, and micromirrors is useful.

Such a functional thin film or thin film device is formed by arelatively high process temperature because of the method for formingit. The substrate 1 must therefore be a highly reliable material whichis resistant to the high process temperature, as described above.

The transferred layer 4 may be a single layer or a composite of aplurality of layers. The transferred layer, such as a thin filmtransistor, may have a given pattern. The formation (deposition) andpatterning of the transferred layer 4 is performed by a predeterminedprocess. The transferred layer 4 is generally formed by a plurality ofsteps.

The transferred layer 4 including thin film transistors is formed by,for example, the methods described in Japanese Patent Publication No.2-50630, and H. Ohsima et al.: International Symposium Digest ofTechnical Papers SID 1983 “B/W and Color LC Video Display Addressed byPoly Si TFTs”.

The thickness of the transferred layer 4 is not limited, and isdetermined in response to various factors, e.g. purpose, function,composition, and characteristics. When the transferred layer 4 includesthin film transistors, its total thickness is preferably 0.5 to 200 μm,and more preferably 0.5 to 10 μm. In the case of other thin films, thepreferable thickness has a wider thickness range, for example, 50 nm to1,000 μm.

The transferred layer 4 is not limited to the above-described thinfilms, and may be thick films, such as coating films and sheets, andtransfer materials or separable materials, such as powder, not formingfilms or layers.

[4] As shown in FIG. 4, an adhesive layer 5 is formed on the transferredlayer (a detached member) 4, and a transfer member 6 is adhered with theadhesive layer 5. Examples of preferable adhesives forming the adhesivelayer 5 include curable adhesives, for example, reactive curingadhesives, heat-hardening adhesives, photo-setting adhesives such asUV-curing adhesives, and anaerobic curing adhesives. Examples of typesof adhesives include epoxys, acrylates, and silicones. The adhesivelayer 5 is formed by, for example, a coating process.

When using a curable adhesive, for example, the curable adhesive isapplied onto the transferred layer 4, the transfer member 6 is adheredthereon, and then the curable adhesive is cured by a method in responseto characteristics of the curable adhesive to adhere the transferredlayer 4 to the transfer member 6. When using a photo-setting adhesive,it is preferable that a transparent transfer member 6 be placed on theuncured adhesive layer 5, and then the substrate 1 and the transfermember 6 be illuminated with light for curing from both sides in orderto secure the curing of the adhesive.

Regardless of the drawings, the adhesive layer 5 may be formed on thetransfer member 6 and then the transferred layer 4 may be adheredthereto. Further, the above-mentioned interlayer may be provided betweenthe transferred layer 4 and the adhesive layer 5. When the transfermember 6 has an adhering function, the formation of the adhesive layer 5may be omitted.

Examples of the transfer member 6 include substrates (plates), andparticularly transparent substrates, although they are not limited tothese substrates. Such substrates may be planar or curved. The transfermember 6 may have inferior characteristics including heat resistance andcorrosion resistance to those of the substrate 1, because, in thepresent invention, the transferred layer 4 is formed on the substrate 1,and the transferred layer 4 is transferred to the transfer member 6,wherein characteristics required for the transfer member 6 areindependent of the conditions, such as temperature, in the formation ofthe transferred layer 4.

Accordingly, when the maximum temperature in the formation of thetransferred layer 4 is Tmax, the transfer member 6 can be formed of amaterial having a glass transition point (Tg) or softening point of Tmaxor less. For example, the transfer member 6 is composed of a materialhaving a glass transition point (Tg) or softening point of 800° C. orless, preferably 500° C. or less and more preferably 320° C. or less.

It is preferable that the transfer member 6 has a given level ofrigidity (mechanical strength), but it may have flexibility orelasticity. Examples of materials for such a transfer member 6 include awide variety of synthetic resins and glass materials, and preferablysynthetic resins and inexpensive glass materials (with low meltingpoints).

Examples of synthetic resins include both thermoplastic resins andthermosetting resins, such as polyolefins, e.g. polyethylene,polypropylene, ethylene-propylene copolymers, and ethylene-vinyl acetatecopolymers (EVAs); cyclic polyolefins; modified polyolefins; polyvinylchloride; polyvinylidene chloride; polystyrene; polyamides;polyamide-imides; polycarbonates; poly-(4-methylpentene-1); ionomers;acrylic resins; polymethyl methacrylate (PMMA);acrylonitrile-butadiene-s- tyrene copolymers (ABS resins);acrylonitrile-styrene copolymers (AS resins); butadiene-styrenecopolymers; polyoxymethylene; polyvinyl alcohol (PVA); ethylene-vinylalcohol copolymers (EVOHs); polyesters, e.g. polyethylene terephthalate(PET), polybutylene terephthalate (PBT), and polycyclohexaneterephthalate (PCT); polyethers; polyether-ketones (PEKs);polyether-ether-ketones (PEEKs); polyether-imides; polyacetals (POMs);polyphenylene oxides; modified polyphenylene oxides; polysulfones;polyphenylene sulfide (PPS); polyether sulfones (PESs); polyarylates;aromatic polyesters (liquid crystal polymers); polytetrafluoroethylene;polyvinylidene fluoride; other fluorine resins; thermoplasticelastomers, e.g. styrene-, polyolefin-, polyvinyl chloride-,polyurethane-, polyester-, polyamide-, polybutadiene-,trans-polyisoprene-, fluorine rubber-, and chlorinatedpolyethylene-type; epoxy resins; phenol resins; urea resins; melamineresins; unsaturated polyesters; silicone resins; and polyurethanes; andcopolymers, blends, and polymer alloys essentially consisting of thesesynthetic resins. One or more of these synthetic resins may be used, forexample, as a composite consisting of at least two layers.

Examples of usable glasses include silicate glass (quartz glass),alkaline silicate glass, soda-lime glass, lead (alkaline) glass, bariumglass, and borosilicate glass. All the types of glass other thansilicate glass have lower boiling points than that of silicate glass,can be readily formed and shaped, and are inexpensive.

When a synthetic resin is used, a large transfer member 6 provided witha complicated shape, such as a curved surface or unevenness, can bereadily formed with low material and production costs. A large,inexpensive device, for example, a liquid crystal display, can thereforebe readily formed.

The transfer member 6 may function as an independent device, such as aliquid crystal cell, or as a part of a device, for example, a colorfilter, an electrode layer, a dielectric layer, an insulating layer, anda semiconductor device. Further, the transfer member 6 may be composedof metal, ceramic, stone, wood, or paper. Alternatively, it may be asurface of a given article (the surface of a watch, clock, airconditioner, or print board), or a surface of a given structure, such asa wall, pillar, post, beam, ceiling, or window glass.

[5] As shown in FIG. 5, the rear side of the substrate 1 (the side 12 ofthe incident light) is irradiated with the incident light 7. Theincident light 7 passes though the substrate 1 and enters the separationlayer 2 through the interface 2 a. As shown in FIG. 6 or FIG. 7,internal and/or interfacial exfoliation occurs in the separation layerand the adhering force is reduced or eliminated. When separating thesubstrate 1 from the transfer member 6, the transferred layer 4 isdetached from the substrate 1 and transferred to the transfer member 6.

FIG. 6 shows a state of the internal exfoliation in the separation layer2, and FIG. 7 shows a state of the interfacial exfoliation at theinterface 2 a on the separation layer 2. The occurrence of the internaland/or interfacial exfoliation presumes that ablation of theconstituents in the separation layer 2 occurs, that gas retained in theseparation layer 2 is released, and that phase transition such asmelting or vaporization occurs immediately after the light irradiation.

The word “ablation” means that solid components (the constituents of theseparation layer 2), which absorbed the incident light, arephotochemically and thermally excited and atoms or molecules in thesolid components are released by the chain scission. The ablation isobserved as phase transition such as melting or vaporization in thepartial or entire constituents of the separation layer 2. Also, finefoaming may be formed by the phase transition, resulting in a decreasedadhering force. The internal and/or interfacial exfoliation of theseparation layer 2 depends on the composition of the separation layer 2and other factors, for example, the type, wavelength, intensity and,range of the incident light 7.

Any type of incident light 7, which causes internal and/or interfacialexfoliation of the separation layer 2, can be used, for example, X-rays,ultraviolet rays, visible rays, infrared rays (heat rays), laser beams,milli-waves, micro-waves, electron rays, and radiations (a-rays, β-rays,and γ-rays). Among them, laser beams are preferable because they caneasily cause exfoliation (ablation) of the separation layer 2.

Examples of lasers generating the laser beams include gas lasers andsolid lasers (semiconductor lasers), and excimer lasers, Nd-YAG lasers,Ar lasers, CO₂ lasers, CO lasers, and He—Ne lasers may be preferablyused. Among them excimer lasers are more preferably used. The excimerlasers output high energy laser beams in a shorter wavelength rangewhich cause ablation in the separation layer 2 within a significantlyshorter time. The separation layer 2 is therefore cleaved substantiallywithout the temperature rise, and thus without deterioration or damageof the adjacent or adjoining interlayer 3, transferred layer 4, andsubstrate 1.

If the ablation of the separation layer 2 is dependent on the wavelengthof the incident light, it is preferable that the wavelength of theincident laser beam be approximately 100 nm to 350 nm.

When exfoliating the separation layer 2 by means of phase transition,for example, gas evolution, vaporization, or sublimation, it ispreferable that the wavelength of the incident laser beam beapproximately 350 nm to 1,200 nm.

Preferably, the energy density of the incident light, and particularlyof the excimer lasers ranges from approximately 10 to 5,000 mJ/cm² andmore preferably approximately 100 to 1,000 mJ/cm². The irradiation timepreferably ranges from 1 to 1,000 nsec., and more preferably from 10 to200 nsec. At an energy density or irradiation time which is lower thanthe lower limit, satisfactory ablation will not occur, whereas at anenergy density or irradiation time which is higher than the upper limit,the transferred layer 4 is adversely affected by the incident lightpassing through the separation layer 2 and interlayer 3.

It is preferable that the incident light 7 including laser beams with auniform intensity be incident on the separation layer. The incidentlight 7 may be incident on the separation layer 2 from the directionperpendicular to the separation layer 2 or from a direction shifted by agiven angle from the perpendicular direction.

When the separation layer 2 has an area which is larger than the areaper scanning of the incident light, the entire separation layer 2 may beirradiated with several scans of incident light. The same position maybe irradiated two or more times. The same position or differentpositions may be irradiated with different types and/or wavelengths ofincident (laser) light beams two or more times.

[6]As shown in FIG. 8, the separation layer 2 remaining on theinterlayer 3 is removed by, for example, washing, etching, ashing orpolishing, or a combination of these methods. Also, the separation layer2 remaining on the substrate 1 is removed in the internal separation ofthe separation layer 2, as shown in FIG. 6.

When the substrate 1 is composed of an expensive or rare material, suchas quartz glass, the substrate 1 is preferably reused. In other words,the present invention is applicable to the substrate to be reused, henceit is useful.

The transfer of the transferred layer 4 to the transfer member 6 iscompleted by the above-mentioned steps. Removal of the interlayer 3adjoining the transferred layer 4 or formation of additional layers maybe employed.

In the present invention, the transferred layer 4 is not directlyseparated as the detached member, but the separation layer 2 adhered tothe transferred layer 4 is exfoliated, hence uniform exfoliation ortransfer is easily, securely, and uniformly achieved regardless ofcharacteristics and conditions of the detached member (transferred layer4). Since the detached member (transferred layer 4) is not damaged, itcan maintain high reliability.

In the embodiment shown in the drawings, a method for transferring thetransferred layer 4 onto the transfer member 6 is described. Theexfoliating method in accordance with the present invention does notalways include such transfer. In this case, a detached member is usedinstead of the transferred layer 4. The detached member may be either alayered material or non-layered material.

The detached member may be used for various purposes, for example,removal (trimming) of unnecessary portions of the thin film(particularly functional thin film), removal of attached members, suchas dust, oxides, heavy metals, and carbon, and recycling of thesubstrate used in the exfoliation method.

The transfer member 6 may be composed of a material having quitedifferent properties from that of the substrate 1 (regardless oftransparency), for example, various types of metal, ceramic, carbon,paper, and rubber, as well as the above-described materials. When thetransfer member 6 does not permit or is not suitable for directformation of the transferred layer 4, the present invention can beusefully applied.

In the embodiment shown in the drawings, the incident light 7 isincident on the substrate 1, however, it may be incident on the sideaway from the substrate 1 when the adhered material (detached member) isremoved or when the transferred layer 4 is not adversely affected byirradiation with the incident light.

Although the exfoliating method in accordance with the present inventionhas been described, the present invention is not limited to thedescription.

For example, the surface of the separation layer 2 may be irradiatedwith the incident light to form a given pattern such that thetransferred layer 4 is cleaved or transferred based on the pattern (afirst method). In this case, in the above-mentioned step [5], the side12 of the incident light of the substrate 1 is masked in response to thepattern before irradiation of the incident light 7, or the positionsirradiated with the incident light 7 are accurately controlled.

The separation layer 2 having a given pattern may be formed instead offorming the separation layer 2 on the entire face 11 of the substrate 1(a second method). In this case, the separation layer 2 having a givenpattern is formed by masking etc. or the separation layer 2 is formed onthe entire surface 11 and is patterned or trimmed by etching etc.

According to the first and second methods, the transferred layer 4 issimultaneously transferred and patterned or trimmed.

Transfer processes may be repeated two or more times by the sameprocedure. When the transfer processes are performed for an even numbersof times, the positions of the front and rear faces of the transferredlayer formed by the last transfer process are the same as those of thetransferred layer formed on the substrate 1 by the first transferprocess.

On a large transparent substrate (for example, having an effective areaof 900 mm by 1,600 mm) as a transfer member 6, transferred layers 4(thin film transistors) formed on small substrates 1 (for example,having an effective area of 45 mm by 40 mm) may be transferred side byside by repeating transfer cycles (for example, approximately 800cycles), so that the transferred layers 4 are formed on the entireeffective area of the large transparent substrate. A liquid crystaldisplay having a size which is the same as that of the large transparentsubstrate can be produced.

Examples of the first embodiment will now be described.

EXAMPLE 1

A quartz substrate with a length of 50 mm, a width of 50 mm, and athickness of 1.1 mm (softening point: 1,630° C., distortion point:1,070° C., and transmittance of excimer laser: approximately 100%) wasprepared, and an amorphous silicon (a-Si) film as a separation layer(laser-absorption layer) was formed on the one side of the quartzsubstrate by a low pressure CVD process (Si₂H₆ gas, 425° C.). Thethickness of the separation layer was 100 nm.

A SiO₂ film as an interlayer was formed on the separation layer by anECR-CVD process (SiH₄+O₂ gas, 100° C.). The thickness of the interlayerwas 200 nm.

A polycrystalline silicon (or polycrystalline silicon) film with athickness of 50 nm as a transferred layer was formed on the interlayerby a CVD process (Si₂H₆ gas). The polycrystalline silicon film waspatterned to form source/drain/channel regions of a thin filmtransistor. After a SiO₂ gate insulating film was formed by thermaloxidation of the surface of the polycrystalline silicon film, a gateelectrode (a structure in which a high melting point metal, such as Mo,was deposited on the polycrystalline silicon) was formed on the gateinsulating film, and source and drain regions were formed by selfalignment by means of ion implantation using the gate electrode as amask. A thin film transistor was thereby formed.

A thin film transistor having similar characteristics can be formed by alow temperature process instead of such a high temperature process. Forexample, an amorphous silicon film with a thickness of 50 nm as atransferred layer was formed on a SiO₂ film as an interlayer on theseparation layer by a low pressure CVD process (Si₂H₆ gas, 425° C.), andthe amorphous silicon film was irradiated with laser beams (wavelength:308 nm) to modify the amorphous silicon into a polycrystalline siliconfilm by crystallization. The polycrystalline silicon film was patternedto form source/drain/channel regions having a given pattern of a thinfilm transistor. After a SiO₂ gate insulating film was deposited on thepolycrystalline silicon film by a low pressure CVD process, a gateelectrode (a structure in which a high melting point metal, such as Mo,was deposited on the polycrystalline silicon) was formed on the gateinsulating film, and source and drain regions were formed by selfalignment by means of ion implantation using the gate electrode as amask. A thin film transistor was thereby formed.

Next, electrodes and leads connected to the source and drain regions andleads connected to the gate electrode were formed, if necessary. Theseelectrodes and leads are generally composed of aluminum, but not for thelimitation. A metal (not melted by laser irradiation in the succeedingstep) having a melting point higher than that of aluminum may be used ifmelting of aluminum is expected in the succeeding laser irradiationstep.

A UV-curable adhesive (thickness: 100 μm) was applied onto the thin filmtransistor, a large, transparent glass substrate (soda glass, softeningpoint: 740° C., distortion point: 511° C.) as a transfer member wasadhered to the adhesive film, and the outer surface of the glasssubstrate was irradiated with ultraviolet rays to fix these layers bycuring the adhesive.

The surface of the quartz substrate was irradiated with Xe—Cl excimerlaser beams (wavelength: 308 nm) to cause exfoliations (internal andinterfacial exfoliation) of the separation layer. The energy density ofthe Xe—Cl excimer laser was 300 mJ/cm², and the irradiation time was 20nano seconds. The excimer laser irradiation methods include a spot-beamirradiation method and a line-beam irradiation method. In the spot-beamirradiation method, a given unit area (for example 8 mm by 8 mm) isirradiated with a spot beam, and the spot irradiation is repeated whileshifting the spot beam by about one-tenth the given unit area. In theline-beam irradiation, a given unit area (for example 378 mm by 0.1 mm,or 378 mm by 0.3 mm (absorbing 90% or more of the incident energy)) isirradiated while shifting the line-beam by about one-tenth the givenunit area. Each of the points of the separation layer is therebyirradiated at least ten times. The entire surface of the quartzsubstrate is irradiated with the laser, while shifting step by step overthe irradiated area.

Next, the quartz substrate was detached from the glass substrate(transfer member) at the separation layer, so that the thin filmtransistor and interlayer formed on the quartz substrate weretransferred onto the glass substrate.

The separation layer remaining on the interlayer on the glass substratewas removed by etching, washing, or a combination thereof. A similarprocess was applied to the quartz substrate for recycling the substrate.

When the glass substrate as the transfer member is larger than thequartz substrate, the transfer from the quartz substrate to the glasssubstrate in accordance with this example can be repeated to form anumber of thin film transistors on different positions on the quartzsubstrate. A larger number of thin film transistors can be formed on theglass substrate by repeated deposition cycles.

EXAMPLE 2

A thin film transistor was transferred as in Example 1, but an amorphoussilicon film containing 20 atomic percent of hydrogen (H) was formed asthe separation layer. The hydrogen content in the amorphous silicon filmwas controlled by the film deposition conditions in the low pressureCVD.

EXAMPLE 3

A thin film transistor was transferred as in Example 1, but a ceramicthin film (composition: PbTiO₃, thickness: 200 nm) as the separationlayer was formed by spin-coating and sol-gel processes.

EXAMPLE 4

A thin film transistor was transferred as in Example 1, but a ceramicthin film (composition: BaTiO₃, thickness: 400 nm) as the separationlayer was formed by a sputtering process.

EXAMPLE 5

A thin film transistor was transferred as in Example 1, but a ceramicthin film (composition: Pb(Zr,Ti)O₃ (PZT), thickness: 50 nm) as theseparation layer was formed by a laser ablation process.

EXAMPLE 6

A thin film transistor was transferred as in Example 1, but a polyimidefilm (thickness: 200 nm) as the separation layer was formed by aspin-coating process.

EXAMPLE 7

A thin film transistor was transferred as in Example 1, but apolyphenylene sulfide film (thickness: 200 nm) as the separation layerwas formed by a spin-coating process.

EXAMPLE 8

A thin film transistor was transferred as in Example 1, but an aluminumfilm (thickness: 300 nm) as the separation layer was formed by asputtering process.

EXAMPLE 9

A thin film transistor was transferred as in Example 2, but Kr—F excimerlaser beams (wavelength: 248 nm) were used as the incident light. Theenergy density of the laser beams was 250 mJ/cm², and the irradiationtime was 20 nano seconds.

EXAMPLE 10

A thin film transistor was transferred as in Example 2, but Nd-YAG laserbeams (wavelength: 1,068 nm) were used as the incident light. The energydensity of the laser beams was 400 mJ/cm², and the irradiation time was20 nano seconds.

EXAMPLE 11

A thin film transistor was transferred as in Example 1, but apolycrystalline silicon film (thickness: 80 nm) as the transferred layerwas formed by a high temperature process at 1,000° C.

EXAMPLE 12

A thin film transistor was transferred as in Example 1, but atransparent polycarbonate substrate (glass transition point: 130° C.) asthe transfer member was used.

EXAMPLE 13

A thin film transistor was transferred as in Example 2, but atransparent AS resin substrate (glass transition point: 70 to 90° C.) asthe transfer member was used.

EXAMPLE 14

A thin film transistor was transferred as in Example 3, but atransparent polymethyl methacrylate substrate (glass transition point:70 to 90° C.) as the transfer member was used.

EXAMPLE 15

A thin film transistor was transferred as in Example 5, but atransparent polyethylene terephthalate substrate (glass transitionpoint: 67° C.) as the transfer member was used.

EXAMPLE 16

A thin film transistor was transferred as in Example 6, but atransparent high-density polyethylene substrate (glass transition point:77 to 90° C.) as the transfer member was used.

EXAMPLE 17

A thin film transistor was transferred as in Example 9, but atransparent polyamide substrate (glass transition point: 145° C.) as thetransfer member was used.

EXAMPLE 18

A thin film transistor was transferred as in Example 10, but atransparent epoxy resin substrate (glass transition point: 120° C.) asthe transfer member was used.

EXAMPLE 19

A thin film transistor was transferred as in Example 11, but atransparent polymethyl methacrylate substrate (glass transition point:70 to 90° C.) as the transfer member was used.

The thin film transistors transferred in Examples 1 to 19 were observedvisually and with a microscope. All the thin film transistors wereuniformly transferred without forming defects and unevenness.

As described above, an exfoliating method in accordance with the presentinvention ensures easy and secure exfoliation regardless ofcharacteristics and conditions of the detached member (transferredlayer), and enables transfer onto various transfer members. For example,a thin film can be formed by transfer on a material not capable of ornot suitable for the direct forming of the thin film, an easily formablematerial, an inexpensive material, and a large article which isdifficult to move.

Materials having thermal and corrosion resistance which is inferior tothat of the substrate, for example, various synthetic resins, and lowmelting point glass materials, can be used as the transfer member. Forexample, in the production of a liquid crystal display including thinfilm transistors (particularly polycrystalline silicon TFTs) formed on atransparent substrate, a large, inexpensive liquid crystal display canbe easily produced by a combination of a heat-resisting quartz glasssubstrate as the substrate, and an inexpensive and formable transparentsubstrate composed of a synthetic resin or a low melting point glass asthe transfer member. Such an advantage will be expected in production ofother devices other than the liquid crystal display.

A transferred layer such as a functional thin film can be formed on aheat-resisting substrate with high reliability, such as a quartzsubstrate, followed by patterning, with maintaining the above-mentionedadvantage. A highly reliable thin film can therefore be formed on atransfer member regardless of the properties of the transfer member.

Second Embodiment

An exfoliating method in accordance with the second embodiment of thepresent invention will now be described in detail with reference to theattached drawings. In the second embodiment, the separation layer 2 ofthe first embodiment has a layered structure including a plurality oflayers.

FIGS. 9 to 16 are cross-sectional views illustrating steps in accordancewith this embodiment in the exfoliating method in accordance with thepresent invention. The steps will be described sequentially withreference to these drawings. Since many matters are common to the firstembodiment, the same parts are identified by the same numeral and adetailed description will be omitted appropriately. Accordingly, matterswhich are different from the first embodiment will be described.

[1] As shown in FIG. 9, a separation layer 2 composed of a compositeincluding a plurality of sub-layers is formed on one face (the face 11)of the substrate 1. In this case, each sub-layer in the separation layer2 is deposited step by step onto the substrate 1 by a method describedbelow. Preferably, the substrate 1 is composed of a transparent materialtransmitting the incident light 7, when the light is incident on theouter surface of the substrate 1.

In this case, the transmittance for the incident light 7 is similar tothat in the first embodiment. Materials for the substrate 1 are commonto the first embodiment. The thickness of the substrate 1 is the same asthat in the first embodiment. It is preferable that the thickness of thesubstrate 1 be uniform at a region for forming the separation layer soas to be uniformly irradiated with the incident light 7. The innersurface 11 and light-incident surface 12 of the substrate 1 may beplanar or curved.

In the present invention, the substrate 1 is detached by exfoliating theseparation layer 2 between the substrate 1 and the transferred layer 4instead of removing the substrate by etching etc., hence the operationcan be easily performed, and the substrate 1 has a wide range ofselectivity, for example, use of a relatively thick substrate.

The separation layer 2 is now described. The separation layer 2 absorbsthe incident light 7 to cause internal and/or interfacial exfoliation ofthe layer. The separation layer 2 includes at least two-sub layershaving different compositions or characteristics, and preferably anoptical absorption layer 21 and other layers having a composition andcharacteristics which are different from the optical absorption layer21. It is preferable that the other layer be a shading layer (reflectionlayer 22) for shading the incident light. The shading layer lies on theside (upper side in the drawings) of the optical absorption layer 21away from the incident light 7, reflects or absorbs the incident light 7to prevent or suppress entry of the incident light into the transferredlayer 4.

In this embodiment, a reflection layer 22 reflecting the incident light7 is formed as the shading layer. It is preferable that the reflectionlayer 22 has a reflectance of 10% or more, and more preferably 30% ormore for the incident light 7. Preferably, such a reflection layer 22 isformed of a metallic thin film including a singularity or plurality ofsub-layers, or a composite including a plurality of thin films havingdifferent refractive indices. In particular, it is composed of metallicthin films in view of easy formability.

Examples of metals suitable for forming a metallic thin film include Ta,W, Mo, Cr, Ni, Co, Ti, Pt, Pd, Ag, Au, and Al; and alloys primarilycontaining at least one of these metals. Examples of preferable elementsto be added to such alloys include Fe, Cu, C, Si, and B. The addition ofthese elements enables control of the thermal conductivity andreflectance of the alloy. Another advantage is easy production of atarget, when forming the reflection layer by physical deposition.Further, alloys can be easily obtained and are inexpensive compared withthe relevant pure metals.

The thickness of the reflection (shading layer) 22 is preferably 10 nmto 10 μm, and more preferably 50 nm to 5 μm, although it is not limitedto such a range. An excessive thickness requires much time for theformation of the reflection layer 22 and the removal of the reflectionlayer 22 which will be performed later. A significantly low thicknessmay cause insufficient shading effects in some film compositions.

The optical absorption layer 21 contributing to the exfoliation of theseparation layer 2 absorbs the incident light 7 to eliminate or reduceinter-atomic or intermolecular adhering forces in the substances in theoptical absorption layer 21 and to cause internal and/or interfacialexfoliation due to an ablation phenomenon. Further, the irradiation withthe incident light 7 may cause exfoliation by the evolution of gas fromthe optical absorption layer 21. A component contained in the opticalabsorption layer 21 is released as gas in one case, or the separationlayer 2 is instantaneously gasified by absorbing the light, and thevapor is released to contribute to the exfoliation in the other case.

The usable compositions of such an optical absorption layer 21 aresimilar to the compositions (1) to (4) which were described in theseparation layer 2 of the first embodiment. In the second embodiment,the following compositions can also be used as the optical absorptionlayer 21.

(5) Organic Polymers:

Usable organic polymers have linkages (which are cut by irradiation ofthe incident light 7), such as —CH—, —CH₂—, —CO— (ketone), —CONH—(amido), —NH—(imido), —COO— (ester), —N═N— (azo), and —CH═N— (isocyano).In particular, any organic polymers having large amounts of suchlinkages can be used. Examples of the organic polymers includepolyolefins, such as polyethylene, and polypropylene; polyimides;polyamides; polyesters; polymethyl methacrylate (PMMA); polyphenylenesulfide (PPS); polyether sulfone (PES); and epoxy resins.

(6) Metals:

Examples of metals include Al, Li, Ti, Mn, In, Sn, and rare earthmetals, e.g. Y, La, Ce, Nd, Pr, Sm, and Gd; and alloys containing atleast one of these metals.

(7) Hydrogen Occluded Alloys:

Examples of hydrogen occluded alloys include rare earth element-basedalloys, such as LaNi₅; and Ti— or Ca—based alloys, in which hydrogen isoccluded.

(8) Nitrogen Occluded Alloys:

Examples of nitrogen occluded alloys include rare earth element-iron,-cobalt, -nickel, and -manganese alloys, such as Sm—Fe and Nd—Co alloys,in which nitrogen is occluded.

The thickness of the optical absorption layer 21 depends on variousfactors, for example, the purpose of the exfoliation, the composition ofthe separation layer 2, the layer configuration, and the formationprocess, and is generally 1 nm to 20 Am, and preferably 10 nm to 2 μm,and more preferably 40 nm to 1 μm. A significantly low thickness of theoptical absorption layer 21 causes deterioration of uniformity of thedeposited film, and thus irregular exfoliation, whereas an excessivethickness requires a large amount of incident light 7 (power) to ensuresatisfactory exfoliation and a longer operational time for removing theseparation layer 2. It is preferable that the thicknesses of the opticalabsorption layer 21 and reflection layer 22 be uniform as much aspossible. For the same reasons, the total thickness of the separationlayer 2 is preferably 2 nm to 50 μm, and more preferably 20 nm to 20 μm.

The method for forming each layer in the separation layer 2 (in thisembodiment, the optical absorption layer 21 and reflection layer 22) isnot limited, and is selected in view of various factors, such as thecomposition and thickness of the film. Examples of the methods includevapor phase deposition processes, such as CVD (including MOCVD, lowpressure CVD, ECR-CVD), evaporation, molecular beam (MB) evaporation,sputtering, ion-plating, and PVD; plating processes, such aselectroplating, dip-plating (dipping), and electroless-plating; coatingprocess, such as a Langmuir-Blodgett process, spin-coating process,spray-coating process, and roll-coating process; printing processes;transfer processes; ink-jet processes; and powder-jet processes. Acombination of these processes may also be usable. The process forforming the optical absorption layer 21 and reflection layer 22 may bethe same or different, and is determined by the composition etc.

For example, when the optical absorption layer 21 is composed ofamorphous silicon (a-Si), it is preferable that the layer be formed by alow pressure CVD process or a plasma CVD process. Alternatively, whenthe optical absorption layer 21 is composed of a ceramic by a sol-gelprocess, or an organic polymer, it is preferable that the layer beformed by a coating process, and particularly a spin-coating process.

The reflection layer 22 composed of a metallic thin film is preferablyformed by evaporation, molecular beam (MB) evaporation, laser ablationdeposition, sputtering, ion plating, and the above-mentioned platingprocesses.

Each layer in the separation layer 2 may be formed by two or more steps,for example, including a layer forming step and an annealing step.

[2] As shown in FIG. 10, an interlayer (underlying layer) 3 is formed onthe separation layer 2.

The interlayer 3 is formed for various purposes, and functions as atleast one layer of, for example, a protective layer which protectsphysically or chemically a transferred layer 4 in production and in use,an insulating layer, a conductive layer, a shading layer of the incidentlight 7, a barrier layer inhibiting migration of any components from orto the transferred layer 4, and a reflection layer.

The composition of the interlayer 3 is determined based on the purpose:For example, the interlayer 3, which is formed between the separationlayer 2 with the amorphous silicon optical absorption layer 21 and thetransferred layer 4 as the thin film transistor, is composed of siliconoxide, e.g. SiO₂, or the interlayer 3 formed between the separationlayer 2 and the PZT transferred layer 4 is composed of a metal, e.g.,Pt, Au, W, Ta, Mo, Al, Cr, or Ti, or an alloy primarily containing sucha metal.

The thickness of the interlayer 3 is similar to that in the firstembodiment. The method for forming the interlayer 3 is also similar tothat in the first embodiment. The interlayer 3 may be composed of two ormore layers having the same composition or different compositions.Alternatively, in the present invention, the transferred layer 4 may bedirectly formed on the separation layer 2 without forming the interlayer3.

[3] As shown in FIG. 11, a transferred layer (detached member) 4 isformed on the interlayer 3. The transferred layer 4 is transferred ontoa transfer member 6 which will be described later, and formed by amethod similar to that for the separation layer 2. The purpose forforming, type, shape, structure, composition, and physical and chemicalcharacteristics of the transferred layer 4 are not limited, and it ispreferable that the transferred layer 4 be a functional thin film or athin film device in view of the purpose and usefulness of the transfer.Examples of the functional thin films and thin film devices have beendescribed in the first embodiment.

Such a functional thin film or thin film device is generally formed at arelatively high process temperature in connection with the manufacturingmethod. As described above, therefore, the substrate 1 must be highlyreliable and resistive to such a high process temperature.

The transferred layer 4 may be composed of a single layer or a pluralityof layers. Additionally, it may be patterned as in the above-describedthin film transistor. The formation (deposition) and patterning of thetransferred layer 4 is performed by a given process according to demand.Such a transferred layer 4 is generally formed by a plurality of steps.The thickness of the transferred layer 4 is also similar to that in thefirst embodiment.

[4] As shown in FIG. 12, an adhesive layer 5 is formed on thetransferred layer (exfoliation layer) 4 to adhere with the transfermember 6 through the adhesive layer 5. Preferred examples of adhesivesfor forming the adhesive layer 5 are identical to those in the firstembodiment. When using a curable adhesive, the curable adhesive isapplied onto the transferred layer 4, a transfer member 6 describedlater is adhered thereto, the curable adhesive is cured by a curingmethod in response to the property to adhere the transferred layer 4with the transfer member 6. In the case using a photo-setting adhesive,it is preferable that a transparent transfer member 6 be placed on theadhesive layer 5, and then the transfer member 6 be irradiated withlight to cure the adhesive. When the substrate 1 is transparent, boththe substrate 1 and the transfer member 6 are preferably irradiated withlight to secure curing of the adhesive.

Instead of the state shown in the drawings, the adhesive layer 5 may beformed on the side of the transfer member 6, and the transferred layer 4may be formed thereon. Further, the above-mentioned interlayer may beformed between the transferred layer 4 and the adhesive layer 5. When,for example, the transfer member 6 has a function as an adhesive, theformation of the adhesive layer 5 can be omitted.

Examples, materials, and characteristics of the transfer member 6 areidentical to those in the first embodiment.

[5] As shown in FIG. 13, the rear side (the incident face 12) of thesubstrate 1 is irradiated with the incident light 7. After the incidentlight 7 passes through the substrate 1, it is radiated to the separationlayer 2 through the interface 2a. In detail, it is absorbed in theoptical absorption layer 21, the part of the incident light 7 notabsorbed in the optical absorption layer 21 is reflected by thereflection layer 22 and passes through the optical absorption layer 21again. The adhering force in the separation layer is reduced oreliminated by the internal and/or interfacial exfoliation, and as shownin FIG. 14 or 15, the transferred layer 4 is detached from the substrateand transferred onto the transfer member 6 when the substrate 1 isseparated from the transfer member 6.

FIG. 14 shows a case of internal exfoliation of the separation layer 2,and FIG. 15 shows a case of interfacial exfoliation at the interface 2 aof the separation layer 2. It is presumed from the occurrence of aninternal and/or interfacial exfoliation that ablation of theconstituents in the optical absorption layer 21 occurs, that gasretained in the optical absorption layer 21 is released, and that phasechange such as melting or vaporization occurs immediately after theirradiation of the light.

Wherein the word “ablation” means that solid components (theconstituents of the optical absorption layer 21), which absorbed theincident light, are photochemically and thermally excited and atoms andmolecules in the solid components are released by the chain scission.The ablation is observed as phase transition such as melting orvaporization in the partial or entire constituents of the opticalabsorption layer 21. Also, fine foaming may be formed by the phasechange, resulting in a reduced adhering force. The internal and/orinterfacial exfoliation of the separation layer 21 depends on the layerconfiguration of the separation layer 2, the composition and thicknessof the optical absorption layer 21 and other factors, for example, thetype, wavelength, intensity and, range of the incident light 7.

Examples of types of the incident light 7 and of apparatuses forgenerating it are identical to those in the first embodiment.

When the ablation in the optical absorption layer 21 depends on thewavelength of the incident light, it is preferable that the wavelengthof the incident laser light ranges from approximately 100 nm to 350 nm.When exfoliating the separation layer 2 by the phase transition such asgas evolution, vaporization, and sublimation, the wavelength of theincident laser light preferably ranges from approximately 350 nm to1,200 nm. The energy density of the incident laser light, andparticularly of the excimer laser light preferably ranges fromapproximately 10 to 5,000 mJ/cm², and more preferably from 100 to 1,000mJ/cm². The preferable irradiation time ranges from 1 to 1,000 nanoseconds, and more preferably 10 to 100 nano seconds. A lower energydensity or a shorter irradiation time may cause insufficient ablation,whereas a higher energy density or a longer irradiation time may causeexcessive breakage of the separation layer 2. It is preferable that theincident light 7 such as laser light be incident such that the intensityis uniform.

The direction of the incident light 7 is not limited to the directionperpendicular to the separation layer 2, and may be shifted by severaldegrees from the perpendicular direction if the area of the separationlayer 2 is larger than the irradiation area per scan of the incidentlight, the entire region of the separation layer 2 may be irradiated twoor more times at the same position. Alternatively, the same position ordifferent positions may be irradiated with different types or differentwavelengths (wavelength regions) of the incident light (laser light).

In this embodiment, the reflection layer 22 is provided at the side ofthe optical absorption layer 21 away from the substrate 1, hence theoptical absorption layer 21 can be effectively irradiated with theincident light 7 without any loss. Further, the irradiation of thetransferred layer 4 with the incident light 7 can be prevented by theshading characteristics of the reflection layer (shading layer),preventing adverse effects, such as the modification and deteriorationof the transferred layer 4.

In particular; since the optical absorption layer 21 is irradiated withthe incident light without loss, the energy density of the incidentlight 7 can be reduced, or in other words, the irradiation area per scancan be increased; a given area of the separation layer 2 can thereforebe exfoliated at decreased irradiation times as an advantage in theproduction process.

[6] As shown in FIG. 16, the separation layer 2 remaining on theinterlayer 3 is removed by, for example, washing, etching, ashing, orpolishing, or a combination thereof. In the internal exfoliation of theseparation layer 2 shown in FIG. 14, the optical absorption layer 21remaining on the substrate 1 can also be removed if necessary.

When the substrate 1 is composed of an expensive or rare material suchas quartz glass, it is preferable that the substrate 1 be reused(recycled). In other words, the present invention is applicable to asubstrate to be reused, and thus is highly useful.

The transfer of the transferred layer 4 onto the transfer member 6 iscompleted by these steps. The removal of the interlayer 3 adjoining thetransferred layer 4 and formation of an additional layer may beincorporated.

The configuration of the separation layer 2 is not limited to that shownin the drawings, and may include that comprising a plurality of opticalabsorption layers which have at least one different property among thecomposition, thickness, and characteristics of the layer. For example,the separation layer 2 may be composed of three layers including a firstoptical absorption layer, a second optical absorption layer, and areflection layer provided therebetween.

The interfaces between the sub-layers forming the separation layer 2 arenot always clearly provided, the composition of the layer, and theconcentration, molecular structure, and physical and chemical propertiesof a given component may continuously change (may have a gradient) nearthe interface.

In this embodiment shown in the drawings, the transfer of thetransferred layer 4 onto the transfer member 6 is described, suchtransfer is not always incorporated in the exfoliating method inaccordance with the present invention.

The exfoliating member can be used for various purposes as described inthe first embodiment. Various transfer members 6 other than thatdescribed above can also be used as in the first embodiment.

When the adhered member (detached member) is removed or when thetransferred layer 4 is not adversely affected by the incident light 7,the incident light 7 is not always incident on the substrate 1, and maybe incident on the side away from the substrate 1. In this case, it ispreferable that the optical absorption layer 21 and the reflection layer22 have a reversed positional relationship in the separation layer 2.

The exfoliating method in accordance with the present invention has beendescribed with reference to this embodiment shown in the drawings, thepresent invention, however, is not limited to this, and permits variousmodifications as in the first embodiment (please refer to thedescription concerning the modifications in the first embodiment).

Examples of the second embodiment will now be described.

EXAMPLE 1

A quartz substrate with a length of 50 mm, a width of 50 mm, and athickness of 1.1 mm (softening point: 1,630° C., distortion point:1,070° C., and transmittance of excimer laser: approximately 100%) wasprepared, and a separation layer having a double-layered structureincluding an optical absorption layer and a reflecting layer was formedon one side of the quartz substrate.

An amorphous silicon (a-Si) film as the optical absorption layer wasformed by a low pressure CVD process (Si₂H₆ gas, 425° C.). The thicknessof the optical absorption layer was 100 nm. A metallic thin filmcomposed of Ta as the reflecting layer was formed on the opticalabsorption layer by a sputtering process. The thickness of thereflection layer was 100 nm, and the reflectance of the laser light was60%.

A SiO₂ film as an interlayer was formed on the separation layer by anECR-CVD process (SiH₄+O₂ gas, 100° C.). The thickness of the interlayerwas 200 nm.

An amorphous silicon film with a thickness of 60 nm as a transferredlayer was formed on the interlayer by a low pressure CVD process (Si₂H₆gas, 425° C.), and the amorphous silicon film was irradiated with laserlight beams (wavelength: 308 nm) to modify the amorphous silicon filminto a polycrystalline silicon film by crystallization. Thepolycrystalline silicon film was subjected to patterning and ion platingto form a thin film transistor.

A UV-curable adhesive (thickness: 100 μm) was applied onto the thin filmtransistor, a large, transparent glass substrate (soda glass, softeningpoint: 740° C., distortion point: 511° C.) as a transfer member wasadhered to the adhesive film, and the outer surface of the glasssubstrate was irradiated with ultraviolet rays to fix these layers bycuring the adhesive.

The surface of the quartz substrate was irradiated with Xe—Cl excimerlaser beams (wavelength: 308 nm) to cause exfoliation (internal andinterfacial exfoliation) of the separation layer. The energy density ofthe Xe—Cl excimer laser was 160 mJ/cm², and the irradiation time was 20nano seconds. The excimer laser irradiation methods include a spot-beamirradiation method and a line-beam irradiation method. In the spot-beamirradiation method, a given unit area (for example 10 mm by 10 mm) isirradiated with a spot beam, and the spot irradiation is repeated whileshifting the spot beam by about one-tenth the given unit area. In theline-beam irradiation, a given unit area (for example 378 mm by 0.1 mm,or 378 mm by 0.3 mm (absorbing 90% or more of the incident energy)) isirradiated with while shifting the line-beam by about one-tenth thegiven unit area. Each of the points of the separation layer is therebyirradiated at least ten times. The entire surface of the quartzsubstrate is irradiated with the laser, while shifting step by step theirradiated area.

Next, the quartz substrate was detached from the glass substrate(transfer member) at the separation layer, so that the thin filmtransistor and interlayer were transferred onto the glass substrate.

The separation layer remaining on the interlayer on the glass substratewas removed by etching, washing, or a combination thereof. A similarprocess was applied to the quartz substrate for recycling the substrate.

EXAMPLE 2

A thin film transistor was transferred as in Example 1, but an amorphoussilicon film containing 18 atomic percent of hydrogen (H) was formed asthe optical absorption layer. The hydrogen content in the amorphoussilicon film was controlled by the film deposition conditions in the lowpressure CVD.

EXAMPLE 3

A thin film transistor was transferred as in Example 1, but a ceramicthin film (composition: PbTiO₃, thickness: 200 nm) as the opticalabsorption layer was formed by spin-coating and sol-gel processes.

EXAMPLE 4

A thin film transistor was transferred as in Example 1, but a ceramicthin film (composition: BaTiO₃, thickness: 400 nm) as the opticalabsorption layer, and a metallic thin film composed of aluminum(thickness: 120 nm, reflectance of laser light: 85%) as the reflectionlayer were formed by a sputtering process.

EXAMPLE 5

A thin film transistor was transferred as in Example 1, but a ceramicthin film (composition: Pb(Zr,Ti)O₃ (PZT), thickness: 50 nm) as theoptical absorption layer was formed by a laser ablation process, and ametallic thin film (thickness: 80 nm, reflectance of laser light: 65%)composed of an Fe—Cr alloy was formed by a sputtering process.

EXAMPLE 6

A thin film transistor was transferred as in Example 1, but a polyimidefilm (thickness: 200 nm) as the optical absorption layer was formed by aspin-coating process.

EXAMPLE 7

A thin film transistor was transferred as in Example 1, but apraseodymium (Pr) film (rare earth metal film) (thickness: 500 nm) asthe optical absorption layer was formed by a sputtering process.

EXAMPLE 8

A thin film transistor was transferred as in Example 2, but Kr—F excimerlaser beams (wavelength: 248 nm) were used as the incident light. Theenergy density of the laser beams was 180 mJ/cm², and the irradiationtime was 20 nano seconds.

EXAMPLE 9

A thin film transistor was transferred as in Example 2, but Ar laserbeams (wavelength: 1,024 nm) were used as the incident light. The energydensity of the laser beams was 250 mJ/cm², and the irradiation time was50 nano seconds.

EXAMPLE 10

A thin film transistor was transferred as in Example 1, but apolycrystalline silicon film (thickness: 90 nm) as the transferred layerwas formed by a high temperature process at 1,000° C.

EXAMPLE 11

A thin film transistor was transferred as in Example 2, but apolycrystalline silicon film (thickness: 80 nm) as the transferred layerwas formed by a high temperature process at 1,030° C.

EXAMPLE 12

A thin film transistor was transferred as in Example 4, but apolycrystalline silicon film (thickness: 80 nm) as the transferred layerwas formed by a high temperature process at 1,030° C.

EXAMPLES 13 TO 20

A series of thin film transistors were transferred as in Examples 12 to19 of the first embodiment.

The thin film transistors transferred in Examples 1 to 20 were observedvisually and with a microscope. All the thin film transistors wereuniformly transferred without forming defects and unevenness.

As described above, the second embodiment in accordance with the presentinvention has advantages shown in the first embodiment, the transferredlayer, such as a thin film transistor, is prevented from adverse affectsby the transmission of the incident light when the separation layerincludes a shading layer, and particularly a reflection layer, and theseparation layer is more effectively exfoliated by the use of thereflecting light from the reflection layer.

Third Embodiment

An exfoliating method in accordance with the third embodiment of thepresent invention will now be described in detail with reference to theattached drawings. In the third embodiment, a thin film device is usedas the detached member or the transferred layer in the first embodiment.

FIGS. 17 to 22 are cross-sectional views illustrating steps inaccordance with this embodiment in the exfoliating method in accordancewith the present invention. Each of the steps of the exfoliating method(transferring method) will be described with reference to thesedrawings. Since many matters are common to the first embodiment, thesame parts are identified by the same numerals and a detaileddescription will be omitted appropriately. Accordingly, matters whichare different from the first embodiment will be described.

[Step 1] As shown in FIG. 17, a separation layer (optical absorptionlayer) is formed on a substrate 100. The substrate 100 and theseparation layer 120 will be described.

(1) Description of the Substrate 100

Preferably, the substrate 100 is composed of a transparent materialwhich transmits light. The light transmittance is identical to the firstembodiment. Also, the material and the thickness of the substrate 100are identical to the first embodiment.

(2) Description of the Separation Layer 120

The separation layer 120 absorbs the incident light to cause internaland/or interfacial exfoliation, and preferably is composed of a materialin which inter-atomic or inter-molecular adhering forces are reduced oreliminated by light irradiation to cause internal and/or interfacialexfoliation based on ablation.

Further, gas causing exfoliating effects may be released from theseparation layer 120 by light irradiation in some cases, that is, a casein which components contained in the separation layer 120 are releasedas gas, and a case in which the separation layer 120 is instantaneouslygasified by absorbing the incident light and the released vaporcontributes to exfoliation. The composition of such a separation layer120 is similar to that in the first embodiment.

Also, the thickness of the separation layer 120 and the method forforming it are similar to those in the first embodiment.

[Step 2] Next, as shown in FIG. 18, a transferred layer (thin filmdevice layer) 140 is formed on the separation layer 120. An enlargedcross-sectional view of the portion K (surrounded by a dotted line inFIG. 18) of the thin film device layer 140 is shown in the right side ofFIG. 18. As shown in the drawing, the thin film device layer 140 iscomposed of a TFT (thin film transistor) formed on a SiO₂ film(interlayer) 142, and the TFT includes source and drain layers 146composed of an n-doped polycrystalline silicon layer, a channel layer144, a gate insulating film 148, a gate electrode 150, an insulatinginterlayer 154, and an electrode composed of, for example, aluminum.

In this embodiment, although the interlayer adjoining the separationlayer 120 is composed of a SiO₂ film, it may be composed of any otherinsulating film, such as Si₃N₄. The thickness of the SiO₂ film(interlayer) is adequately determined based on the purpose for theformation and its functions, and ranges generally from approximately 10nm to 5 82 m, and preferably 40 nm to 1 μm. The interlayer is formed forvarious purposes, and functions as at least one of a protective layerphysically or chemically protecting the transferred layer 140, aninsulating layer, a conductive layer, a shading layer to laser light, abarrier layer for preventing migration, and a reflection layer.

In some cases, the transferred layer (thin film device layer) 140 may bedirectly formed on the separation layer 120, by omitting the formationof the interlayer, such as the SiO₂ film.

The transferred layer (thin film device layer) 140 includes a thin filmdevice such as a TFT, as shown in the right side of FIG. 18. As well asa TFT, other thin film devices shown in the first embodiment can also beused. These thin film devices are generally formed at a relatively highprocess temperature inherent to the formation method. Thus, as describedabove, the substrate 100 must have high reliability and must beresistant to the process temperature.

[Step 3] As shown in FIG. 19, the thin film device layer 140 is adheredto a transfer member 180 using an adhesive layer 160. Preferableexamples of adhesives forming the adhesive layer 160 are described inthe first embodiment.

When using a curable adhesive, for example, the curable adhesive isapplied onto the transferred layer (thin film device layer) 140, thetransfer member 180 is adhered thereto, the curable adhesive is cured bya curing method in response to the property to adhere the transferredlayer (thin film device layer) 140 with the transfer member 180. In thecase where a photo-setting adhesive is used, the outer surface of thetransparent substrate 100 or transparent transfer member 180 (or bothouter surfaces of the transparent substrate and transparent transfermember) is irradiated with light. A photo-setting adhesive, which barelyaffects the thin film device layer, is preferably used as the adhesive.

Instead of the method shown in the drawing, the adhesive layer 160 maybe formed on the transfer member 180 and the transferred layer (thinfilm device layer) 140 may be adhered thereto. Alternatively, theformation of the adhesive layer 160 can be omitted when the transfermember 180 has adhesive characteristics.

Examples of the transfer members 180 are described in the firstembodiment.

[Step 4] As shown in FIG. 20, the rear side of the substrate 100 isirradiated with light. The light passing through the substrate 100 isincident on the separation layer 120. As a result, internal and/orinterfacial exfoliation, which reduces or eliminates the adheringforces, occurs. It is presumed from the occurrence of the internaland/or interfacial exfoliation in the separation layer 120 that ablationof the constituents in the separation layer 120 occurs, that gasretained in the separation layer 120 is released, and that phasetransition such as melting or vaporization occurs immediately after thelight irradiation.

The word “ablation” has the same meaning as in the first embodiment

The incident light is identical to the light used in the firstembodiment. In particular, excimer lasers are preferably used. Theexcimer lasers output high energy laser beams in a shorter wavelengthrange which cause ablation in the separation layer 120 within asignificantly shorter time. The separation layer 120 is thereforecleaved substantially without the temperature rise, and thus withoutdeterioration or damage of the adjacent or adjoining transfer member180, and substrate 100.

If the ablation of the separation layer 120 is dependent on thewavelength of the incident light, it is preferable that the wavelengthof the incident laser beam be approximately 100 nm to 350 nm.

FIG. 23 is a graph of transmittance vs. wavelength of light in thesubstrate 100. As shown in the graph, the transmittance increasessteeply at a wavelength of 300 nm. In such a case, light beams having awavelength of higher than 300 nm (for example, Xe—Cl excimer laser beamshaving a wavelength of 308 nm) are used. When exfoliating the separationlayer 120 by means of phase transition, for example, gas evolution,vaporization, or sublimation, it is preferable that the wavelength ofthe incident laser beam be approximately 350 nm to 1,200 nm.

The energy density of the incident laser light beam, and particularly ofthe excimer laser light beam, is similar to that in the firstembodiment.

When the light passing through the separation layer 120 reaches thetransferred layer 140 and adversely affects the layer, a metallic film124 composed of tantalum (Ta) etc. may be formed on the separation layer(laser absorption layer) 120. The laser light passing through theseparation layer 120 is completely reflected on the interface with themetallic film 124, and thus does not affect the thin film deviceprovided on the metallic film. It is preferable that the intensity ofthe incident light such as laser light be uniform. The direction of theincident light is not always perpendicular to the separation layer 120,and may be shifted by a given angle from the perpendicular direction.

If the area of the separation layer 120 is larger than the irradiationarea per scan of the incident light, the entire region of the separationlayer 120 may be irradiated two or more times at the same position.Alternatively, the same position or different positions may beirradiated with different types or different wavelengths (wavelengthregions) of the incident light (laser light).

Next, as shown in FIG. 21, the substrate 100 is detached from theseparation layer 120 by applying a force to the substrate 100. A part ofthe separation layer may remain on the substrate after the detachment,not shown in FIG. 21.

As shown in FIG. 22, the residual separation layer 120 is removed byetching, ashing, washing, polishing or a combination thereof. Thetransferred layer (thin film device layer) 140 is thereby transferredonto the transfer member 180. Also, the moiety of the separation layerremaining on the substrate 100 is removed. When the substrate 100 iscomposed of an expensive or rare material such as quartz glass, it ispreferably reused (recycled). That is, the present invention isapplicable to the substrate 100 to be reused, and is useful.

The transfer of the transferred layer (thin film device layer) 140 ontothe transfer member 180 is completed by these steps. The SiO₂ filmadjoining the transferred layer (thin film device layer) 140 may beremoved, or a conductive layer for wiring and/or a protective film maybe formed on the transferred layer 140.

In the present invention, the transferred layer (thin film device layer)140 is not directly separated as the detached member, but the separationlayer adhered to the transferred layer (thin film device layer) 140 isexfoliated, hence uniform exfoliation or transfer is easily, securely,and uniformly achieved regardless of characteristics and conditions ofthe detached member (transferred layer 140). Since the detached member(transferred layer 140) is not damaged during the exfoliating operation,it can maintain high reliability.

Examples 1 to 19 in the first embodiment can also be applied to thethird embodiment.

Fourth Embodiment

The fourth embodiment includes a modification of a step in the thirdembodiment.

Formation of an Amorphous Silicon Layer in the Step 1

When the separation layer 120 is composed of amorphous silicon (a-Si),it is preferably formed by a chemical vapor deposition (CVD) process,and particularly by a low pressure (LP) CVD process, compared withplasma CVD, atmospheric pressure (AP) CVD, and ECR processes. Forexample, an amorphous silicon layer formed by the plasma CVD processcontains a relatively large quantity of hydrogen. The presence ofhydrogen makes the ablation of the amorphous silicon layer easy, whereinhydrogen is released from the amorphous silicon layer at a temperatureof higher than 350° C. The evolution of hydrogen during the step formingthe thin film device may cause exfoliation of the film. Further, theplasma CVD film has relatively low adhesiveness, hence the substrate 100may be detached from the transferred layer 140 in the wet washing stepin the production of the device. In contrast, the LPCVD film has nopossibility of evolution of hydrogen and has sufficient adhesiveness.

The thickness of the amorphous silicon layer 120 as the separation layerwill be described with reference to FIG. 39. In FIG. 39, the horizontalaxis represents the thickness of the amorphous silicon layer, and thevertical axis represents the optical energy absorbed in this layer. Asdescribed above, when the amorphous silicon layer is irradiated withlight, ablation occurs.

The word “ablation” means that solid components (the constituents of theseparation layer 120), which absorbed the incident light, arephotochemically and thermally excited and atoms and molecules in thesolid components are released by the chain scission. The ablation isobserved as phase transition such as melting or vaporization in thepartial or entire constituents of the separation layer 120. Also, finefoaming may be formed by the phase change, resulting in a decreasedadhering force.

The absorbed energy required for the ablation decreases with a decreasedthickness, as shown in FIG. 39.

Accordingly, the thickness of the amorphous silicon layer 120 as theseparation layer is reduced in this embodiment. The energy of the lightincident on the amorphous silicon layer 120 is thereby reduced,resulting in lower energy consumption and miniaturization of the lightsource unit.

The thickness level of the amorphous silicon layer 120 as the separationlayer will now be investigated. As shown in FIG. 39, the absorbed energyrequired for the ablation decreases as the thickness of amorphoussilicon decreases. According to the present inventors investigation, itis preferable that the thickness be 25 nm or less, hence ablation canoccur by the power of a general light source unit. Although the lowerlimit of the thickness is not limited, a lower limit of 5 nm may bedetermined in view of the secure formation and adhesiveness of theamorphous silicon layer. Accordingly, the preferable thickness of theamorphous silicon layer 120 ranges from 5 nm to 25 nm, and morepreferably 15 nm or less for achieving further energy saving and higheradhesiveness. The optimum range of the thickness is 11 nm or less, andthe absorbed energy required for the ablation can be significantlydecreased near the thickness.

Fifth Embodiment

The fifth embodiment includes a modification of a step in the third orfourth embodiment.

Reinforcement of the Transfer Member in the Step 3

Although the transfer member 180 has preferably a certain amount ofrigidity as a mechanical property, it may have flexibility orelasticity. Such a mechanical property of the transfer member 180 isdetermined in consideration of the following point. When the separationlayer 120 is irradiated with light, the constituent material of theseparation layer 120 is photochemically or thermally excited, andmolecules or atoms on and in the layer are cleaved to release moleculesor atoms outside. It is preferable that the transfer member 180 hasmechanical strength which is resistant to the stress acting on the upperportion of the separation layer 120 accompanied by the release ofmolecules or atoms. A deformation or breakage at the upper portion ofthe separation layer 120 can be thereby prevented.

Such mechanical strength may be imparted not only to the transfer member180, but also to at least one layer lying above the separation layer120, that is, the transferred layer 140, the adhesive layer 160, and thetransfer member 180. The materials for and thicknesses of thetransferred layer 140, adhesive layer 160, and transfer member 180 canbe determined in order to achieve such mechanical strength.

When a combination of the transferred layer 140, adhesive layer 160 andtransfer member 180 does not have sufficient mechanical strength, areinforcing layer 132 may be formed at an appropriate position above theseparation layer 120, as shown in FIGS. 42(A) to 42(E).

The reinforcing layer 132 shown in FIG. 42(A) is provided between theseparation layer 120 and the transferred layer 140. After formingexfoliation in the separation layer 120 and detaching the substrate 100,the reinforcing layer 132 can be removed together with the remainingseparation layer 120 from the transferred layer 140. As shown in FIG.42(B), the reinforcing layer 132 provided above the transferred layer180 can also be removed from the transferred layer 180, after theseparation layer 120 is cleaved. The reinforcing layer 132 shown in FIG.42(C) intervenes as, for example, an insulating layer in the transferredlayer 140 composed of a plurality of layers. Each reinforcing layer 132shown in FIGS. 42(D) and 42(E) is placed under or on the adhesive layer160. In such a case, it cannot be removed later.

Sixth Embodiment

The sixth embodiment includes a modification of a step in any one of thethird, fourth, and fifth embodiments.

Formation of an Amorphous Silicon-Based Optical Absorption Layer as theSeparation Layer in the Step 4

It is preferable that a method shown in FIG. 40 or 41 be employedinstead of the method shown in FIG. 38. In FIG. 40, an amorphous siliconlayer 120 is employed as the separation layer, and another amorphoussilicon layer 126 is also employed as a silicon-based optical absorptionlayer. In order to separate these two amorphous silicon layers 120 and126, a silicon oxide (SiO₂) film intervenes as a silicon-basedintervening layer. Even if the-incident light passes through theamorphous silicon layer 120 as the separation layer, the transmittedlight is absorbed in the amorphous silicon layer 126 as thesilicon-based optical absorption layer. As a result, the thin filmdevice provided thereon is not adversely affected. Since the twoadditional layers 126 and 128 are composed of silicon, metalliccontamination etc. does not occur in an established conventional filmdeposition technology.

When the thickness of the amorphous silicon layer 120 as the separationlayer is larger than the thickness of the amorphous silicon layer 126 asthe optical absorption layer, exfoliation in the amorphous silicon layer126 can be securely prevented. Regardless of such a relationship of thethicknesses, however, the optical energy incident on the amorphoussilicon layer 126 is considerably lower than the optical energy incidenton the amorphous silicon layer 120 as the separation layer, no ablationoccurs in the amorphous silicon layer 126.

FIG. 41 shows a case providing a silicon-based optical absorption layer130 composed of a different material from that of the separation layer120, wherein the silicon-based intervening layer is not alwaysnecessary.

When a countermeasure to optical leakage in the separation layer 120 isemployed as shown in FIG. 40 or 41, adverse effects to the thin filmdevice can be securely prevented even if the optical absorption energyfor exfoliating the separation layer 120 is high.

Seventh Embodiment

The seventh embodiment includes a modification of a step in any one ofthe third to sixth embodiments.

Modification of Irradiation with Light in the Step 4

A method of irradiation with light, which is suitable for a case nothaving a metallic film 124 shown in FIG. 38 and does not affect the thinfilm device, will now be described with reference to the drawings fromFIG. 43 onwards.

FIGS. 43 and 44 show a method for irradiating almost the entireseparation layer 120 with light. In each drawing, the number of scanningtimes of line beams is represented by N, and beam scanning is performedsuch that the region 20(N) irradiated with the N-th line beam 10 doesnot overlap with the region 20(N+1) irradiated with the (N+1)-th linebeam 10. As a result, a low- or non-irradiation region 30 which issignificantly narrower than each irradiated region is formed between thetwo adjacent regions 20(N) and 20(N+1).

When the line beam 10 is moved to the direction shown by the arrow A inrelation to the substrate 100 while radiating the beam, alow-irradiation region 30 is formed. Alternatively, when the beam is notradiated during such a movement, a non-irradiation region 30 is formed.

If the regions irradiated by different line beams overlap with eachother, the separation layer 120 is irradiated with an excessive amountof incident light which is larger than that required for internal and/orinterfacial exfoliation. When the light leaked from the separation layer120 is incident on the transferred layer 140 including a thin filmdevice, electrical and other characteristics of the thin film devicewill deteriorate.

In the method shown in FIGS. 43 and 44, the separation layer 120 is notirradiated with such excessive light, hence the original characteristicsinherent to the thin film device can be maintained after the it istransferred onto the transfer member. Although exfoliating does notoccur in the low- or non-irradiation region 30 in the separation layer120, the adhesiveness between the separation layer 120 and the substrate100 can be satisfactorily reduced by exfoliating in the regionsirradiated with the line beams.

An example of beam scanning in view of the intensity of the line beam 10will be described with reference to FIGS. 44 to 47.

In FIG. 44, beam scanning is performed such that the region 20(N)irradiated with the N-th line beam 10 overlaps with the region 20(N+1)irradiated with the (N+1)-th line beam 10. A doubly-irradiated region 40is therefore formed between the two adjacent regions 20(N) and 20(N+1).

The following description is an explanation of why leakage caused byexcessive incident light does not occur in the doubly-irradiated region40 in the separation layer 120 and why the original characteristics ofthe thin film device can be maintained.

FIGS. 46 and 47 are graphs of distributions of optical intensity vs. theposition of the two adjacent line beams 10 and 10 in beam scanning.

In accordance with the distribution of the optical intensity shown inFIG. 46, each line beam 10 has a flat peak 10 a having a maximumintensity at a predetermined region including the beam center. The twoadjacent line beams 10 and 10 are scanned such that the twocorresponding flat peaks 10 a do not overlap with each other.

In contrast, according to the distribution of the optical intensityshown in FIG. 47, each line beam 10 has a beam center with a maximumintensity, wherein the optical intensity decreases at a point distantfrom the beam center. The two adjacent line beams 10 and 10 are scannedsuch that the two beam-effective regions having an intensity which is90% of the maximum intensity of each line beam 10 do not overlap witheach other.

As a result, the total dose (summation of products of opticalintensities by irradiated times at each position) of the light beamsincident on the doubly-irradiated region 40 is lower than that of theflat region or beam-effective region. The doubly-irradiated region 40,therefore, will first be cleaved at the second irradiation of the beams,and this does not correspond to the excessive irradiation of beam. Ifthe relevant region of the separation layer is cleaved at the firstirradiation, the intensity in the second irradiation of the light beam,which is incident on the thin film device, is reduced, hencedeterioration of the electrical characteristics of the thin film devicecan be prevented or significantly reduced to a practical level.

In order to suppress leakage of light in the doubly-irradiated region40, it is preferable that the intensity of each beam which is incidenton the doubly-irradiated region 40 be less than 90%, more preferably 80%or less, and most preferably 50% or less of the maximum intensity at thecenter of each beam. When the intensity of the beam is significantlyhigh so that exfoliation occurs at an intensity which is half (50%) themaximum intensity of the beam, overlapping at regions in which theintensity is higher than half of the maximum intensity may be avoided.

Such irradiation modes can also be applicable to beam shapes, such as aspot beam, other than a line beam. In the spot beam scanning, verticaland horizontal relationships between the adjacent irradiated regionsmust be taken into account.

The direction of the incident light including laser light is not limitedto the direction perpendicular to the separation layer 120, and may beshifted by a given angle from the perpendicular direction as long as theintensity of the incident light is substantially uniform in theseparation layer 120.

An example in accordance with the present invention will now bedescribed. The example corresponds to a modification of the laserirradiation in Example 1 of the third embodiment.

MODIFIED EXAMPLE 1

A quartz substrate with a length of 50 mm, a width of 50 mm, and athickness of 1.1 mm (softening point: 1,630° C., distortion point:1,070° C., and transmittance of excimer laser: approximately 100%) wasprepared, and an amorphous silicon (a-Si) film as a separation layer(laser-absorption layer) was formed on the one side of the quartzsubstrate by a low pressure CVD process (Si₂H₆ gas, 425° C.). Thethickness of the separation layer was 100 nm.

A SiO₂ film as an interlayer was formed on the separation layer by anECR-CVD process (SiH₄+O₂ gas, 100° C.). The thickness of the interlayerwas 200 nm.

A polycrystalline silicon (or polycrystalline silicon) film with athickness of 50 nm as a transferred layer was formed on the interlayerby a CVD process (Si₂H₆ gas). The polycrystalline silicon film waspatterned to form source/drain/channel regions of a thin filmtransistor. After a SiO₂ gate insulating film was formed by thermaloxidation of the surface of the polycrystalline silicon film, a gateelectrode (a structure in which a high melting point metal, such as Mo,was deposited on the polycrystalline silicon) was formed on the gateinsulating film, and source and drain regions were formed by selfalignment by means of ion implantation using the gate electrode as amask. A thin film transistor was thereby formed.

A thin film transistor having similar characteristics can be formed by alow temperature process instead of such a high temperature process. Forexample., an amorphous silicon film with a thickness of 50 nm as atransferred layer was formed on a SiO₂ film as an interlayer on theseparation layer by a low pressure CVD process (Si₂H₆ gas, 425° C.), andthe amorphous silicon film was irradiated with laser beams (wavelength:308 nm) to modify the amorphous silicon into a polycrystalline siliconfilm by crystallization. The polycrystalline silicon film was patternedto form source/drain/channel regions having a given pattern of a thinfilm transistor. After a SiO₂ gate insulating film was deposited on thepolycrystalline silicon film by a low pressure CVD process, a gateelectrode (a structure in which a high melting point metal, such as Mo,was deposited on the polycrystalline silicon) was formed on the gateinsulating film, and source and drain regions were formed by selfalignment by means of ion implantation using the gate electrode as amask. A thin film transistor was thereby formed.

Next, electrodes and leads connected to the source and drain regions andleads connected to the gate electrode were formed, if necessary. Theseelectrodes and leads are generally composed of aluminum, but not for thelimitation. A metal (not melted by laser irradiation in the succeedingstep) having a melting point higher than that of aluminum may be used ifmelting of aluminum is expected in the succeeding laser irradiationstep.

A UV-curable adhesive (thickness: 100 μm) was applied onto the thin filmtransistor, a large, transparent glass substrate (soda glass, softeningpoint: 740° C., distortion point: 511° C.) as a transfer member wasadhered to the adhesive film, and the outer surface of the glasssubstrate was irradiated with ultraviolet rays to fix these layers bycuring the adhesive.

The surface of the quartz substrate was irradiated with Xe—Cl excimerlaser beams (wavelength: 308 nm) to cause exfoliation (internal andinterfacial exfoliation) of the separation layer. The energy density ofthe Xe—Cl excimer laser was 250 mJ/cm², and the irradiation time was 20nano seconds. The excimer laser irradiation methods include a spot-beamirradiation method and a line-beam irradiation method. In the spot-beamirradiation method, a given unit area (for example 8 mm by 8 mm) isirradiated with a spot beam, and the spot irradiation is repeated whilescanning the spot beam such that irradiated regions do not overlap witheach other (in the vertical and horizontal directions), as shown in FIG.43. In the line-beam irradiation, a given unit area (for example 378mm±˜0.1 mm, or 378 mm±˜0.3 mm (absorbing 90% or more of the incidentenergy)) is irradiated while scanning the line-beam such that irradiatedregions do not overlap with each other, as shown in FIG. 43.Alternatively, irradiation may be performed such that the totalintensity of the beams is reduced in the doubly-irradiated region.

Next, the quartz substrate was detached from the glass substrate(transfer member) at the separation layer, so that the thin filmtransistor and interlayer formed on the quartz substrate weretransferred onto the glass substrate. The separation layer remaining onthe interlayer on the glass substrate was removed by etching, washing,or a combination thereof. A similar process was applied to the quartzsubstrate for recycling it.

When the glass substrate as the transfer member is larger than thequartz substrate, the transfer from the quartz substrate to the glasssubstrate in accordance with this example can be repeated to form anumber of thin film transistors on different positions on the quartzsubstrate. A larger number of thin film transistors can be formed on theglass substrate by repeated deposition cycles.

Eighth Embodiment

An exfoliating method in accordance with the eighth embodiment of thepresent invention will now be described in detail with reference to theattached drawings. In the eighth embodiment, the exfoliation member ortransferred layer in any one of the first to seventh embodiments iscomposed of a CMOS-TFT.

FIGS. 24 to 34 are cross-sectional views of the steps in the exfoliatingmethod in this embodiment.

[Step 1] As shown in FIG. 24, a separation layer (for example, anamorphous silicon layer formed by a LPCVD process) 120, an interlayer(for example, SiO₂ film) 142, and an amorphous silicon layer (forexample, formed by a LPCVD process) 143 are deposited in that order on asubstrate (for example, a quartz substrate) 100, and then the entireamorphous silicon layer 143 is irradiated with laser light beams toanneal the layer. The amorphous, silicon layer 143 is thereby modifiedinto a polycrystalline silicon layer by recrystallization.

[Step 2] As shown in FIG. 25, the polycrystalline silicon layer formedby laser annealing is patterned to form islands 144 a and 144 b.

[Step 3] As shown in FIG. 26, gate insulating films 148 a and 148 b areformed to cover the islands 144 a and 144 b, for example, by a CVDprocess.

[Step 4] As shown in FIG. 27, gate electrodes 150 a and 150 b composedof polycrystalline silicon or metal are formed.

[Step 5] As shown in FIG. 28, a mask layer 170 composed of a polyimideresin etc. is formed, and for example, boron (B) is ion-implanted byself-alignment using the gate electrode 150 b and the mask layer 170 asmasks. p-Doped layers 172 a and 172 b are thereby formed.

[Step 6] As shown in FIG. 29, a mask layer 174 composed of a polyimideresin etc. is formed, and for example, phosphorus (P) is ion-implantedby self-alignment using the gate electrode 150 a and the mask layer 174as masks. n-Doped layers 146 a and 146 b are thereby formed.

[Step 7] As shown in FIG. 30, an insulating interlayer 154 is formed,contact holes are selectively formed, and then electrodes 152 a to 152 dare formed.

The formed CMOS-TFT corresponds to the transferred layer (thin filmdevice) shown in FIGS. 18 to 22. A protective film may be formed on theinsulating interlayer 154.

[Step 8] As shown in FIG. 31, an epoxy resin layer 160 as an adhesivelayer is formed on the CMOS-TFT, and then the TFT is adhered to thetransfer member (for example, a soda-glass substrate) 180 with the epoxyresin layer 160. The epoxy resin is cured by heat to fix the transfermember 180 and the TFT.

A photo-polymeric resin which is a UV-curable adhesive may also be usedas the adhesive layer 160. In such a case, the transfer member 180 isirradiated with ultra-violet rays to cure the polymer.

[Step 9] As shown in FIG. 32, the rear surface of the substrate 100 isirradiated with, for example, Xe—Cl excimer laser beams in order tocause internal and/or interfacial exfoliation of the separation layer120.

[Step 10] As shown in FIG. 33, the substrate 100 is detached.

[Step 11] The separation layer 120 is removed by etching. As shown inFIG. 34, thereby, the CMOS-TFT is transferred onto the transfer member180.

Ninth Embodiment

The use of transfer technologies of thin film devices described in thefirst to eighth embodiments enables the formation of a microcomputercomposed of thin film devices on a given substrate, for example, asshown in FIG. 35(a). In FIG. 35(a), on a flexible substrate 182 composedof plastic etc., a CPU 300 provided with a circuit including thin filmdevices, a RAM 320, an input-output circuit 360, and a solar battery 340having PIN-junction of amorphous silicon for supplying electrical powerto these circuits are mounted. Since the microcomputer in FIG. 35(a) isformed on the flexible substrate, it is resistive to bending, as shownin FIG. 35(b), and to dropping because of its light weight.

Tenth Embodiment

An active matrix liquid crystal display device, shown in FIGS. 36 and37, using an active matrix substrate can be produced by a transfertechnology of any one of the first to fourth embodiments.

As shown in FIG. 36, the active matrix liquid crystal display device isprovided with an illumination source 400 such as a back light, apolarizing plate 420, an active matrix substrate 440, a liquid crystal460, a counter substrate 480, and a polarizing plate 500.

When a flexible active matrix substrate 440 and a counter substrate 480such as plastic film are used, a flexible, lightweight active matrixliquid crystal panel resistant to impact can be achieved by substitutinga reflecting liquid crystal panel using a reflective plate instead ofthe illumination source 400. When the pixel electrode is formed ofmetal, the reflecting plate and the polarizing plate 420 are notrequired.

The active matrix substrate 440 used in this embodiment is adriver-built-in active matrix substrate in which a TFT is provided in apixel section 442 and a driver circuit (a scanning line driver and adata line driver) 444 is built in.

A circuit of a main section of the active matrix liquid crystal displaydevice is shown in FIG. 37. As shown in FIG. 37, in a pixel section 442,a gate is connected to a gate line G1, and either a source or a drain isconnected to a data line D1. Further, the pixel section 442 includes aTFT (M1) and a liquid crystal 460, wherein the other of the source anddrain is connected to the liquid crystal 460. A driver section 444includes a TFT (M2) formed by the same process as for the TFT (M1) inthe pixel section 442.

The active matrix substrate 440 including TFTs (M1 and M2) can be formedby the transferring method in accordance with either the third or fourthembodiment.

INDUSTRIAL APPLICABILITY

In accordance with the present invention as described above, varioustypes of exfoliation members (detached members) capable of forming onsubstrates are transferred onto transfer members which are other thanthe substrates which are used in the formation of the exfoliationmembers so that the exfoliation members are arranged on the transfermembers which are other than the substrates used in the formation of theexfoliation members. Accordingly, the present invention is applicable toproduction of various devices including liquid crystal devices andsemiconductor integrated circuits.

1. A method for transferring comprising: forming a first layer on afirst member, the forming of the first layer including an irradiation ofa second member that includes the first layer with a light, theirradiating being carried out with a scanning of the light, the scanninglight of the light being performed such that a first area of the secondmember irradiated with the light overlaps at least a second area of thesecond member that is irradiated with the light before the first area isirradiated with the light.
 2. A method for transferring a transferredlayer including a thin film device on a substrate onto a transfer membercomprising: a first step of forming a separation layer on saidsubstrate; a second step of forming said transferred layer includingsaid thin film device on said separation layer; a third step of adheringsaid transferred layer including said thin film device to said transfermember with an adhesive layer; a fourth step of irradiating saidseparation layer with light from a side of said substrate through saidsubstrate causing exfoliation in said separation layer and/or at aninterface of said separation layer and said substrate; and a fifth stepof detaching said substrate from said separation layer; wherein saidfourth step includes sequential scanning of N beams for locallyirradiating said separation layer, such that a region irradiated by anN-th beam (wherein N is an integer of 1 or more) does not overlap withregions irradiated by other beans.
 3. A method for transferring atransferred layer including a thin film device on a substrate on asubstrate onto a transfer member comprising: a first step of forming aseparation layer on said substrate; a second step of forming saidtransferred layer including said thin film device on said separationlayer; a third step of adhering said transferred layer including saidthin film device on said transfer member with an adhesive layer; afourth step of irradiating said separation layer with light from a sideof said substrate through said substrate causing exfoliation in saidseparation layer and/or at an interface of said separation layer andsaid substrate; and a fifth step of detaching said substrate from saidseparation layer; wherein said fourth step includes sequential scanningof N beams for locally irradiating said separation layer, such that eachbeam has a flat peak region having a maximum optical intensity in acenter, and flat peak region irradiated by the N-th beam (wherein N isan integer of 1 or more) does not overlap with other irradiated flatpeak regions irradiated by other beams.
 4. A method for transferring atransferred layer including a thin film device on a substrate on asubstrate onto a transfer member comprising: a first step of forming aseparation layer on said substrate; a second step of forming saidtransferred layer including said thin film device on said separationlayer; a third step of adhering said transferred layer including saidthin film device on said transfer member with an adhesive layer; afourth step of irradiating said separation layer with light from a sideof said substrate through said substrate causing exfoliation in saidseparation layer and/or at an interface of said separation layer andsaid substrate; and a fifth step of detaching said substrate from saidseparation layer; wherein said fourth step includes sequential scanningof N beams for locally irradiating said separation layer, such that eachbeam has a maximum optical intensity in a central region, and aneffective region irradiated by the N-th beam (wherein N is an integer of1 or more) having an intensity, which is 90% or more of a maximumintensity, does not overlap with other effective regions irradiated byother beams.